Physics, Chemistry & Genetics Practice Quiz

Enthusiast Minor Test Quiz - 50 MCQs

Physics, Chemistry & Genetics Practice Quiz

Question 1
Figure here shows the vertical cross-section of a vessel filled with a liquid of density $\rho$. The normal thrust per unit area on the walls of the vessel at point $P$ at depth $(H-h)$ below the free surface of the liquid is:
Correct Answer: Option (3)
Explanation
The pressure (normal thrust per unit area) at any point in a stationary fluid depends only on the depth $d$ of that point below the free surface. Since point $P$ is at depth $d = H-h$, the normal thrust per unit area is $(H-h)\rho g$.
Question 2
In a hydraulic lift, used at a service station, the radius of the large and small piston are in the ratio of $20 : 1$. What mass placed on the small piston will be sufficient to lift a car of mass $1500\text{ kg}$?
Correct Answer: Option (1)
Explanation
By Pascal's Law, the pressure transmitted is equal: $\frac{F_1}{A_1} = \frac{F_2}{A_2} \implies \frac{m_1 g}{\pi r^2} = \frac{m_2 g}{\pi R^2}$
$$m_1 = m_2 \left(\frac{r}{R}\right)^2 = 1500 \left(\frac{1}{20}\right)^2 = \frac{1500}{400} = 3.75\text{ kg}$$.
Question 3
Two vessels A and B of different shapes have the same base area and are filled with water up to the same height $h$. The force exerted by water on the base is $F_A$ for vessel A and $F_B$ for vessel B. The respective weights of the water filled in vessels are $W_A$ and $W_B$. If vessel A is wider at the top than the bottom, and vessel B is narrower at the top, then:
Correct Answer: Option (2)
Explanation
The pressure at the base of both vessels is the same ($P = h\rho g$) since the liquid columns have equal height. Because the base areas $A$ are identical, the normal force exerted by the water on the base is equal for both: $F_A = F_B = P \times A = h\rho g A$. However, since vessel A is wider at the top, it holds a greater volume of water, meaning its weight is larger: $W_A > W_B$.
Question 4
The density of ice is $x\text{ g/cm}^3$ and that of water is $y\text{ g/cm}^3$. What is the change in volume in $\text{cm}^3$, when $m\text{ g}$ of ice melts?
Correct Answer: Option (4)
Explanation
Initial volume of ice is $V_{\text{ice}} = \frac{m}{\text{density of ice}} = \frac{m}{x}$.
Final volume of water is $V_{\text{water}} = \frac{m}{\text{density of water}} = \frac{m}{y}$.
The change in volume is:
$$\Delta V = V_{\text{water}} - V_{\text{ice}} = \frac{m}{y} - \frac{m}{x} = m \left(\frac{1}{y} - \frac{1}{x}\right)$$
Question 5
A block of steel of size $5\text{ cm} \times 5\text{ cm} \times 5\text{ cm}$ is weighed in water. If the relative density of steel is $7$, its apparent weight is:
Correct Answer: Option (1)
Explanation
Volume of block $V = 5 \times 5 \times 5 = 125\text{ cm}^3$.
Relative density ($RD$) = $7$, so density of steel = $7\text{ g/cm}^3$.
Weight in air = $V \times d_{\text{steel}} = 125 \times 7\text{ gf} = 5 \times 5 \times 5 \times 7\text{ gf}$.
Upthrust (buoyancy force) = $V \times d_{\text{water}} = 125 \times 1\text{ gf} = 5 \times 5 \times 5 \times 1\text{ gf}$.
Apparent weight in water = Weight in Air - Upthrust:
$$W_{\text{apparent}} = 125 \times 7\text{ gf} - 125 \times 1\text{ gf} = 125 \times (7-1)\text{ gf} = 6 \times 5 \times 5 \times 5\text{ gf}$$.
Question 6
A tank is filled with water up to height $H$. Water is allowed to come out of a hole $P$ in one of the walls at a depth $D$ below the surface of water. The horizontal distance $x$ in terms of $H$ and $D$ is best expressed as:
Correct Answer: Option (2)
Explanation
By Torricelli's theorem, the velocity of efflux is $v = \sqrt{2gD}$.
The time taken for the water to fall a distance of $(H-D)$ to the ground is $t = \sqrt{\frac{2(H-D)}{g}}$.
The horizontal range is:
$$x = v \times t = \sqrt{2gD} \times \sqrt{\frac{2(H-D)}{g}} = 2\sqrt{D(H - D)}$$.
Question 7
A fixed cylindrical vessel is filled with water up to height $H$. A hole is bored in the wall at a depth $h$ from the free surface of water. For maximum horizontal range, $h$ must be equal to:
Correct Answer: Option (3)
Explanation
The horizontal range of the water is given by $x = 2\sqrt{h(H-h)}$.
To find the maximum range, we differentiate $y = h(H-h) = hH - h^2$ with respect to $h$ and set it to zero:
$$\frac{dy}{dh} = H - 2h = 0 \implies h = \frac{H}{2}$$.
Question 8
The diameter of a brass rod is $4\text{ mm}$ and Young’s modulus of brass is $9 \times 10^{10}\text{ N/m}^2$. The force required to stretch it by $0.1\%$ of its length is:
Correct Answer: Option (1)
Explanation
Radius $r = 2\text{ mm} = 2 \times 10^{-3}\text{ m}$.
Area of cross-section $A = \pi r^2 = \pi (2 \times 10^{-3})^2 = 4\pi \times 10^{-6}\text{ m}^2$.
Strain $\frac{\Delta L}{L} = 0.1\% = 10^{-3}$.
From Young's Modulus formula:
$$F = Y \times A \times \frac{\Delta L}{L} = (9 \times 10^{10}) \times (4\pi \times 10^{-6}) \times 10^{-3} = 360\pi\text{ N}$$.
Question 9
The load versus elongation graph for four wires of the same material and length is plotted. The thinnest wire is represented by the line with:
Correct Answer: Option (2)
Explanation
Since Young's modulus $Y = \frac{\text{Stress}}{\text{Strain}} = \frac{F/A}{\Delta L/L}$, we can write the load $F$ as:
$$F = \left(\frac{Y A}{L}\right) \Delta L$$
The slope of the load ($F$) vs elongation ($\Delta L$) graph is $\frac{Y A}{L}$. For wires of the same material ($Y$) and length ($L$), the slope is directly proportional to the cross-sectional area $A$. Therefore, the thinnest wire (smallest $A$) will have the lowest slope.
Question 10
If the potential energy of a spring is $V$ on stretching it by $2\text{ cm}$, then its potential energy when it is stretched by $10\text{ cm}$ will be:
Correct Answer: Option (4)
Explanation
Potential energy of a spring is $U = \frac{1}{2} k x^2$, where $x$ is the elongation.
Therefore, potential energy is proportional to the square of elongation ($U \propto x^2$).
Ratio of P.E. is:
$$\frac{U_2}{U_1} = \left(\frac{x_2}{x_1}\right)^2 = \left(\frac{10}{2}\right)^2 = 5^2 = 25 \implies U_2 = 25 V$$.
Question 11
The terminal velocity of a sphere moving through a viscous medium is:
Correct Answer: Option (3)
Explanation
The terminal velocity ($v_t$) of a spherical body of radius $r$ falling through a viscous medium is given by Stokes' Law:
$$v_t = \frac{2 r^2 (\rho - \sigma) g}{9 \eta}$$
where $\rho$ and $\sigma$ are the densities of the sphere and the fluid respectively, and $\eta$ is the coefficient of viscosity. This shows that terminal velocity is directly proportional to the square of the radius of the sphere ($v_t \propto r^2$).
Question 12
A small steel ball falls through a syrup at constant speed of $10\text{ cm/s}$. If the steel ball is pulled upwards with a force equal to twice its effective weight, how fast will it move upwards?
Correct Answer: Option (1)
Explanation
When the ball falls at terminal velocity $v = 10\text{ cm/s}$, the downward effective weight $W_{\text{eff}}$ is balanced by the upward viscous drag force $F_v$: $F_v = W_{\text{eff}} = 6\pi \eta r (10)$.
When pulled upwards with an external force $F = 2W_{\text{eff}}$, the net upward force on the ball is:
$$F_{\text{net}} = F - W_{\text{eff}} = 2W_{\text{eff}} - W_{\text{eff}} = W_{\text{eff}}$$
Since the net upward driving force is exactly equal to the downward effective weight, the upward terminal velocity must be identical to the downward terminal velocity, which is $10\text{ cm/s}$.
Question 13
A parallel plate capacitor is charged and the charging battery is then disconnected. If the plates of the capacitor are moved further apart by means of an insulated handle, then:
Correct Answer: Option (4)
Explanation
Because the battery is disconnected, the charge $Q$ on the plates must remain constant.
Capacitance is $C = \frac{\epsilon_0 A}{d}$. As the distance $d$ increases, the capacitance $C$ decreases.
Since $V = Q/C$, the voltage $V$ increases.
The electrostatic energy stored is $U = \frac{Q^2}{2C}$. Since $Q$ is constant and $C$ decreases, the energy $U$ increases (the external work done in pulling the plates apart is stored as electrostatic potential energy).
Question 14
Two metallic charged spheres whose radii are $20\text{ cm}$ and $10\text{ cm}$ respectively, have each $150\mu\text{C}$ positive charge. The common potential after they are connected by a conducting wire is:
Correct Answer: Option (1)
Explanation
Total charge $Q_{\text{total}} = Q_1 + Q_2 = 150\mu\text{C} + 150\mu\text{C} = 300\mu\text{C} = 3 \times 10^{-4}\text{ C}$.
Total capacitance $C_{\text{total}} = C_1 + C_2 = 4\pi \epsilon_0 R_1 + 4\pi \epsilon_0 R_2 = 4\pi \epsilon_0 (R_1 + R_2)$.
Since $\frac{1}{4\pi \epsilon_0} = 9 \times 10^9\text{ N m}^2/\text{C}^2$:
$$C_{\text{total}} = \frac{R_1 + R_2}{9 \times 10^9} = \frac{0.2 + 0.1}{9 \times 10^9} = \frac{0.3}{9 \times 10^9} = \frac{1}{3 \times 10^{10}}\text{ F}$$
Common potential $V = \frac{Q_{\text{total}}}{C_{\text{total}}} = \frac{3 \times 10^{-4}}{1 / (3 \times 10^{10})} = 9 \times 10^6\text{ V}$.
Question 15
A parallel plate capacitor has rectangular plates of $400\text{ cm}^2$ area and are separated by a distance of $2\text{ mm}$ with air as medium. What charge will appear on the plates if a $200\text{ V}$ potential difference is applied across the condenser?
Correct Answer: Option (2)
Explanation
Area $A = 400\text{ cm}^2 = 400 \times 10^{-4}\text{ m}^2 = 4 \times 10^{-2}\text{ m}^2$.
Distance $d = 2\text{ mm} = 2 \times 10^{-3}\text{ m}$.
Capacitance $C = \frac{\epsilon_0 A}{d} = \frac{(8.854 \times 10^{-12}) \times (4 \times 10^{-2})}{2 \times 10^{-3}} = 1.77 \times 10^{-10}\text{ F}$.
Charge $Q = C V = (1.77 \times 10^{-10}\text{ F}) \times 200\text{ V} = 3.54 \times 10^{-8}\text{ C}$.
Question 16
There are two metallic plates of a parallel plate capacitor. One plate is given a charge $+q$ while the other is earthed. Points $P$ (inside the capacitor), $P_1$ (outside the earthed plate), and $P_2$ (outside the charged plate) are taken. The electric field is non-zero at:
Correct Answer: Option (1)
Explanation
When one plate is given a charge $+q$ and the other is earthed, a charge of $-q$ is induced on the inner surface of the earthed plate. Outside the plates (at $P_1$ and $P_2$), the electric fields produced by the $+q$ and $-q$ charges are equal in magnitude and opposite in direction, so they cancel out completely ($E = 0$). Inside the plates (at $P$), the fields due to both plates point in the same direction and add up to $E = \frac{\sigma}{\epsilon_0} \neq 0$.
Question 17
An air capacitor $C$ connected to a battery of emf $V$ acquires a charge $q$ and energy $E$. The capacitor is disconnected from the battery and a dielectric slab of dielectric constant $k$ is placed between the plates. Which of the following statements is correct?
Correct Answer: Option (3)
Explanation
Since the capacitor is disconnected from the battery, the charge must remain constant ($q' = q$).
Inserting a dielectric slab increases the capacitance to $C' = kC$.
The new potential difference is $V' = q/C' = q/(kC) = V/k$, which represents a decrease.
The new stored energy is $E' = \frac{q^2}{2C'} = \frac{q^2}{2kC} = E/k$, which also decreases.
Question 18
Two identical metal plates are given positive charges $Q_1$ and $Q_2$ ($Q_2 < Q_1$) respectively. If they are now brought close together to form a capacitor with capacitance $C$, the potential difference between them is:
Correct Answer: Option (4)
Explanation
When plates with charges $Q_1$ and $Q_2$ are placed parallel to each other, the charges distribute on the outer and inner surfaces. The charge on the outer surfaces of both plates is $\frac{Q_1 + Q_2}{2}$.
The charge on the inner surface of the first plate is $Q_1 - \frac{Q_1 + Q_2}{2} = \frac{Q_1 - Q_2}{2}$.
The charge on the inner surface of the second plate is $Q_2 - \frac{Q_1 + Q_2}{2} = -\frac{Q_1 - Q_2}{2}$.
Since the electric field inside is due solely to the inner charges, the potential difference is:
$$V = \frac{q_{\text{inner}}}{C} = \frac{Q_1 - Q_2}{2C}$$.
Question 19
In a series connection of two capacitors of values $4\mu\text{F}$ and $6\mu\text{F}$ connected to a voltage source, the ratio of the potential difference across the $4\mu\text{F}$ capacitor to that across the $6\mu\text{F}$ capacitor is:
Correct Answer: Option (2)
Explanation
In a series connection, the charge $Q$ on both capacitors is the same. Since $V = Q/C$, the potential difference across a capacitor is inversely proportional to its capacitance ($V \propto 1/C$).
Thus, the ratio of potential differences is:
$$\frac{V_4}{V_6} = \frac{C_6}{C_4} = \frac{6}{4} = \frac{3}{2}$$.
Question 20
Tautomerism is not exhibited by which of the following compounds?
Correct Answer: Option (2)
Explanation
To exhibit keto-enol tautomerism, a carbonyl compound must have at least one $\alpha$-hydrogen atom attached to an $sp^3$ hybridised carbon. In Benzaldehyde ($\text{C}_6\text{H}_5\text{CHO}$), the carbonyl carbon is directly bonded to an $sp^2$ carbon of the benzene ring, which has no $\alpha$-hydrogen. Thus, it cannot undergo tautomerism.
Question 21
Electrolysis of an aqueous solution of sodium succinate ($^{\ominus}\text{OOC-CH}_2-\text{CH}_2-\text{COO}^{\ominus} 2\text{Na}^{\oplus}$) via Kolbe's electrolysis yields which major gaseous organic product at the anode?
Correct Answer: Option (2)
Explanation
During the electrolysis of sodium succinate, the succinate anions discharge at the anode to form succinate radicals. Decarboxylation of this radical produces a biradical ($\cdot\text{CH}_2-\text{CH}_2\cdot$), which rapidly undergoes internal radical coupling to form a double bond, yielding ethylene ($\text{CH}_2=\text{CH}_2$) gas.
Question 22
Consider the electrophilic addition of $\text{HCl}$ to $3,3$-dimethylbut-1-ene: $(\text{CH}_3)_3\text{C}-\text{CH}=\text{CH}_2 + \text{HCl} \rightarrow \text{Product}$. The major product of this reaction is:
Correct Answer: Option (1)
Explanation
Protonation of the alkene yields the secondary carbocation $(\text{CH}_3)_3\text{C}-\text{CH}^+-\text{CH}_3$. To increase stability, a $1,2$-methyl shift occurs from the adjacent quaternary carbon, forming a highly stable tertiary carbocation: $(\text{CH}_3)_2\text{C}^+-\text{CH(CH}_3)_2$. Attack of the chloride nucleophile then gives the rearranged major product, $2$-chloro-$2,3$-dimethylbutane.
Question 23
Propene reacts with bromine water ($\text{Br}_2/\text{H}_2\text{O}$) to form $1,2$-dibromopropane. This anti-addition reaction occurs via the formation of which intermediate?
Correct Answer: Option (2)
Explanation
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium (specifically, a cyclic bromonium) ion intermediate. This bulky three-membered ring blocks one face of the molecule, preventing syn-addition. The halide ion (acting as a nucleophile) must attack from the opposite face in a backside attack, resulting exclusively in anti-addition.
Question 24
Arrange the following alkenes in decreasing order of reactivity towards electrophilic addition reactions (such as with $\text{HCl}$):
(P) $\text{CH}_3-\text{C(CH}_3)=\text{CH}_2$
(Q) $p\text{-MeO}-\text{C}_6\text{H}_4-\text{C(CH}_3)=\text{CH}_2$
(R) $p\text{-NH}_2-\text{C}_6\text{H}_4-\text{C(CH}_3)=\text{CH}_2$:
Correct Answer: Option (3)
Explanation
The rate-determining step in electrophilic addition is the formation of the carbocation. Electron-donating groups stabilize the carbocation intermediate via resonance ($+M$ effect) or inductive effects. The amino group ($-\text{NH}_2$ in R) is a stronger electron-donating resonance group than the methoxy group ($-\text{OCH}_3$ in Q), both of which are far superior to the hyperconjugative electron donation of the alkyl group in P. Thus, the stability of the intermediate carbocation (and the reaction rate) follows the order: R > Q > P.
Question 25
For a given unsymmetrical alkene, Hydroboration-Oxidation (using $\text{BH}_3\cdot\text{THF} / \text{H}_2\text{O}_2, \text{OH}^-$) and Oxymercuration-Demercuration (using $\text{Hg(OAc)}_2, \text{H}_2\text{O} / \text{NaBH}_4$) yield which products respectively?
Correct Answer: Option (1)
Explanation
Hydroboration-Oxidation is a clean method for the **anti-Markovnikov** addition of water across a double bond without carbocation rearrangements. Oxymercuration-Demercuration represents a highly efficient **Markovnikov** addition of water, also proceeding without skeletal rearrangements.
Question 26
Reaction of $1,3$-butadiene with $1\text{ mole}$ of $ ext{HCl}$ at a very low temperature (around $-80^\circ\text{C}$ under kinetic control) yields which major organic product?
Correct Answer: Option (1)
Explanation
Addition of halogen acids to conjugated dienes is temperature-dependent. At low temperatures (kinetic control), the reaction rate is determined by the activation energy. The $1,2$-addition product ($3$-chlorobut-1-ene) forms much faster due to the proximity of the chloride ion to the newly formed carbocation, making it the major product at low temperatures.
Question 27
Addition of bromine water ($\text{Br}_2 / \text{H}_2\text{O}$) to *trans*-but-2-ene undergoes an anti-addition mechanism. The stereochemical nature of the resulting bromohydrin product is a:
Correct Answer: Option (2)
Explanation
Halohydrin formation involves anti-addition. When unsymmetrical groups (like $-\text{Br}$ and $-\text{OH}$) add in an anti fashion to a symmetrical *trans*-alkene, it results in the formation of a pair of non-superimposable enantiomers in equal amounts, creating a **racemic mixture**.
Question 28
When acetone is treated with an excess of ethanol in the presence of dry hydrochloric acid gas, the resulting gem-dialkoxy organic compound is a:
Correct Answer: Option (2)
Explanation
Ketones react with excess monohydric alcohols (like ethanol) under acidic conditions (dry $\text{HCl}$ gas) to undergo nucleophilic addition followed by dehydration. This replaces the carbonyl oxygen with two alkoxy groups, forming a stable **ketal** (which is a subclass of acetals) named $2,2$-diethoxypropane.
Question 29
Arrange the following carbonyl compounds in decreasing order of their reactivity towards nucleophilic addition reactions:
Formaldehyde (I), Acetaldehyde (II), Acetone (III), Acetophenone (IV):
Correct Answer: Option (1)
Explanation
Reactivity of carbonyl compounds towards nucleophilic addition is governed by steric and electronic factors. Sterically, bulkier groups around the carbonyl carbon hinder the approach of the nucleophile. Electronically, electron-donating groups (like methyl in II and III, and phenyl in IV) reduce the partial positive charge on the carbonyl carbon, making it less electrophilic. Therefore, formaldehyde is the most reactive, and acetophenone is the least reactive: I > II > III > IV.
Question 30
Reaction of a secondary amine ($\text{R}_2\text{NH}$) with a carbonyl compound containing at least one $\alpha$-hydrogen atom undergoes dehydration to yield:
Correct Answer: Option (3)
Explanation
Primary amines react with carbonyls to form imines (containing a $\text{C}=\text{N}$ bond). Secondary amines ($\text{R}_2\text{NH}$) lack a second hydrogen on the nitrogen atom to form a carbon-nitrogen double bond. Instead, after nucleophilic attack, elimination of water occurs by abstracting an $\alpha$-hydrogen from the adjacent carbon, creating a carbon-carbon double bond, yielding an **enamine**.
Question 31
In Ninhydrin ($1,2,3$-indantrione), which carbonyl group is highly reactive towards nucleophilic addition, forming a stable hydrate in water?
Correct Answer: Option (1)
Explanation
The central carbonyl group at C-2 is flanked on both sides by strongly electron-withdrawing terminal carbonyl groups (at C-1 and C-3). The strong $-I$ effect of these adjacent groups makes the C-2 carbon highly electrophilic (electron-deficient). In addition, hydration of the C-2 carbon relieves steric and electrostatic repulsion between the three adjacent polar carbonyl groups, making the central C-2 hydrate extremely stable.
Question 32
Which of the following generic structures represents a hemiacetal functional group?
Correct Answer: Option (1)
Explanation
A hemiacetal is a carbon compound characterized by a single carbon atom that is simultaneously bonded to one hydroxyl group ($-\text{OH}$) and one ether group ($-\text{OR}$). An acetal has two ether groups on the same carbon ($\text{R-CH(OR')}_2$).
Question 33
Propane ($\text{CH}_3\text{CH}_2\text{CH}_3$) can be synthesized in the cleanest and highest yield without secondary alkane byproducts using which of the following reactions?
Correct Answer: Option (1)
Explanation
The Wurtz reaction of mixed alkyl halides yields a complex mixture of alkanes (ethane, propane, butane) because of random coupling. Corey-House synthesis is specifically designed for the coupling of two different alkyl groups to synthesize unsymmetrical alkanes in high purity: $\text{R-X} + \text{R'}_2\text{CuLi} \rightarrow \text{R-R'} + \text{R'-Cu} + \text{LiX}$.
Question 34
Which of the following orders is correct regarding s-block elements and their compounds?
Correct Answer: Option (1)
Explanation
The thermal stability of alkaline earth metal sulfates increases down the group as the size of the metal cation increases. A larger cation has lower charge density and lower polarizing power, causing less distortion (polarization) of the large sulfate anion, which makes the ionic lattice thermally more stable.
Question 35
Both the water solubility and thermal stability increase down the group for which alkaline earth metal compounds?
Correct Answer: Option (1)
Explanation
For Group 2 metal hydroxides, the lattice energy decreases much faster than the hydration energy down the group as cation size increases. This causes the solubility of hydroxides to increase down the group ($\text{Be(OH)}_2 < \text{Mg(OH)}_2 < \text{Ca(OH)}_2 < \text{Sr(OH)}_2 < \text{Ba(OH)}_2$). Their thermal stability also increases down the group as their basic character increases.
Question 36
Select the incorrect order of properties for the given alkaline earth metal compounds:
Correct Answer: Option (3)
Explanation
Thermal stability of carbonates increases down the group as polarizing power of the cation decreases. Therefore, $\text{BeCO}_3$ decomposes at a much lower temperature than $\text{MgCO}_3$ or $\text{CaCO}_3$. This means the **ease of oxide formation on heating** is highest for $\text{BeCO}_3$ and decreases down: $\text{BeCO}_3 > \text{MgCO}_3 > \text{CaCO}_3$. Thus, the order in (3) is incorrect.
Question 37
Which of the following compounds does not exhibit hydrogen bonding?
Correct Answer: Option (2)
Explanation
Potassium phosphite ($\text{K}_2\text{HPO}_3$) contains a direct phosphorous-hydrogen ($\text{P-H}$) bond, which is non-polar and cannot participate in hydrogen bonding. Potassium hydrogen phosphate ($\text{K}_2\text{HPO}_4$) contains an active polar $-\text{O-H}$ group that participates in H-bonding.
Question 38
Which of the following compounds exhibits the highest lattice energy?
Correct Answer: Option (3)
Explanation
Lattice energy ($U$) is proportional to the product of ionic charges ($q_1 q_2$) and inversely proportional to the interionic distance. For $\text{Al}_2\text{O}_3$, the charges are $+3$ and $-2$, giving a charge product of $3 \times 2 = 6$, which is much higher than $\text{AlF}_3$ ($3 \times 1 = 3$), $\text{Na}_2\text{O}$ ($2$), or $\text{CaF}_2$ ($2$).
Question 39
Which of the following hydride is a covalent polymeric solid?
Correct Answer: Option (2)
Explanation
Due to the small size and high polarizing power of Beryllium, $\text{BeH}_2$ is covalent. In the solid state, it polymerizes into an infinite chain where beryllium atoms are bridged by hydrogen atoms (three-center two-electron bonds).
Question 40
In the Solvay process for the commercial manufacture of sodium carbonate, which raw material is used to supply carbon dioxide and quicklime?
Correct Answer: Option (1)
Explanation
Limestone ($\text{CaCO}_3$) is thermally decomposed in a kiln to produce $\text{CO}_2$ gas (used in the carbonating tower) and calcium oxide (CaO, quicklime). Quicklime is then slaked with water to form slaked lime, which recovers ammonia from ammonium chloride.
Question 41
Which pair of metals directly combines with atmospheric nitrogen ($\text{N}_2$) on heating to form solid ionic nitrides?
Correct Answer: Option (1)
Explanation
Due to their diagonal relationship, Lithium (Group 1) and Magnesium (Group 2) have small ionic radii and high charge densities. This allows them to overcome the high bond energy of the nitrogen triple bond ($N\equiv N$) and directly form stable solid nitrides ($\text{Li}_3\text{N}$ and $\text{Mg}_3\text{N}_2$).
Question 42
Which of the following statements about beryllium chloride ($\text{BeCl}_2$) is incorrect?
Correct Answer: Option (3)
Explanation
Beryllium chloride ($\text{BeCl}_2$) is indeed covalent and electron-deficient. In the vapour phase at high temperatures, it exists as a planar chloro-bridged dimer ($\text{Be}_2\text{Cl}_4$). In the solid state, it polymerizes to form a chain structure where beryllium is tetrahedrally coordinated and $sp^3$ hybridized. Thus, statement (3) is incorrect.
Question 43
Which of the following properties of alkaline earth metals increases down the group with increasing atomic number?
Correct Answer: Option (2)
Explanation
Solubility of Group 2 hydroxides increases down the group. Conversely, the solubility of Group 2 sulfates decreases down the group. Electronegativity and ionization potentials also decrease down the group due to increasing atomic radius and shielding effect.
Question 44
Which of the following compounds does *not* produce Oxygen gas ($\text{O}_2$) upon thermal decomposition?
Correct Answer: Option (1)
Explanation
Ammonium dichromate decomposes on heating to yield nitrogen gas, green chromium(III) oxide, and water vapor:
$$\text{(NH}_4)_2\text{Cr}_2\text{O}_7 \xrightarrow{\Delta} \text{N}_2 + \text{Cr}_2\text{O}_3 + 4\text{H}_2\text{O}$$
No oxygen is released. The other salts decompose to release oxygen.
Question 45
When a violet-flowered pea plant of unknown genotype is crossed with a homozygous recessive white-flowered plant, the progeny exhibits violet and white flowers in an exact $1 : 1$ ratio. This test cross proves that:
Correct Answer: Option (1)
Explanation
A test cross involves crossing an individual of dominant phenotype with a homozygous recessive individual. If the dominant parent is homozygous dominant (WW), $100\%$ of the offspring will be heterozygous violet (Ww). If the dominant parent is heterozygous (Ww), the offspring will segregate in a $1:1$ ratio ($\text{Ww}$ violet and $\text{ww}$ white).
Question 46
Mendel's Law of Segregation (Principle of purity of gametes) is biologically based on the physical separation of alleles during:
Correct Answer: Option (1)
Explanation
Segregation of alleles occurs during gamete formation in meiosis. Specifically, homologous chromosomes (each carrying one allele of a gene) separate and move to opposite poles during **Anaphase I of meiosis**, ensuring that each gamete receives only one of the two alleles.
Question 47
A child of blood group 'O' ($ii$) has a father of blood group 'B'. What must be the genotype of the father?
Correct Answer: Option (2)
Explanation
A child of blood group 'O' has the homozygous recessive genotype $ii$. The child must inherit one recessive allele $i$ from the mother and one from the father. Since the father has blood group 'B', he must possess at least one dominant $I^B$ allele. Therefore, the father's genotype must be heterozygous $I^B i$.
Question 48
The recombination frequency between genes A and B is $9\%$, between A and C is $17\%$, and between B and C is $26\%$. What is the linear arrangement of these genes on the chromosome?
Correct Answer: Option (2)
Explanation
Recombination frequencies are directly proportional to map distances on a chromosome. Since B and C have the highest recombination frequency ($26\%$), they are the furthest apart. Gene A must lie between them since the distance B-A ($9\%$) plus A-C ($17\%$) equals the total distance B-C ($26\%$, map units/centiMorgans). Thus, the linear order is B – A – C.
Question 49
Which of the following human genetic disorders is inherited as an **autosomal dominant** trait?
Correct Answer: Option (2)
Explanation
Myotonic dystrophy is an autosomal dominant muscular disorder. Phenylketonuria is autosomal recessive. Haemophilia is a sex-linked (X-linked) recessive disorder, and Turner's syndrome is an aneuploidy (monosomy, 45,XO).
Question 50
Which nuclear structure was discovered by Henking in $1891$ during insect spermatogenesis, which we now know as the X-chromosome?
Correct Answer: Option (1)
Explanation
In 1891, German biologist Hermann Henking observed a specific nuclear structure during insect spermatogenesis that was received by only half of the sperm cells. He called this structure the **'X-body'**. Later scientists identified this as the X-chromosome, establishing its role in genetic sex determination.