Mock Test 2: MCQs with Explanations

1. Which of the following statements regarding hydrides is not correct?

• (a) Ionic hydrides are crystalline, non-volatile and non-conducting in solid state.
• (b) Electron-deficient hydrides act as Lewis acids or electron acceptors.
• (c) Elements of group-13 form electron-deficient hydrides.
• (d) Elements of group 15-17 form electron-precise hydrides.

Correct Answer: (d)

Explanation: Elements of group 14 form electron-precise hydrides. Groups 15-17 form electron-rich hydrides because they possess lone pairs of electrons.

2. Which one of the following reactions demonstrates that $H_{2}O_{2}$ acts as an oxidising agent in the basic medium?

• (a) $Na_{2}CO_{3} + H_{2}O_{2} \rightarrow Na_{2}O_{2} + H_{2}O + CO_{2}$
• (b) $2[Fe(CN)_{6}]^{3-} + H_{2}O_{2} + 2OH^{-} \rightarrow 2[Fe(CN)_{6}]^{4-} + 2H_{2}O + O_{2}$
• (c) $Mn^{2+} + H_{2}O_{2} + 2OH^{-} \rightarrow MnO_{2} + 2H_{2}O$
• (d) $MnO_{2} + H_{2}O_{2} + 2H^{+} \rightarrow Mn^{2+} + 2H_{2}O + O_{2}$

Correct Answer: (c)

Explanation: In basic medium, $H_{2}O_{2}$ oxidises $Mn^{2+}$ to $MnO_{2}$. In reaction (b), it acts as a reducing agent.

3. The aqueous solution of an unknown sodium salt gives white turbidity with HCl, decolourises iodine solution, and gives a white ppt with $AgNO_{3}$ which finally becomes black on standing. The salt is:

• (a) sodium sulphite
• (b) sodium sulphide
• (c) sodium bisulphite
• (d) sodium thiosulphate.

Correct Answer: (d)

Explanation: Sodium thiosulphate ($Na_{2}S_{2}O_{3}$) reacts with HCl to give a white turbidity of sulphur. It decolourises $I_{2}$ and forms a white ppt of $Ag_{2}S_{2}O_{3}$ with $AgNO_{3}$ which turns black ($Ag_{2}S$).

4. When $NaBH_{4}$ is dissolved in water:

• (a) $Na^{+}$ and $BH_{4}^{-}$ ions are formed which are stable
• (b) it decomposes with the evolution of $H_{2}$
• (c) $BH_{4}^{-}$ is formed initially decomposed to give $OH^{-}$ ions
• (d) $NaH$ and $B_{2}H_{6}$ are produced.

Correct Answer: (b)

Explanation: Sodium borohydride decomposes in water to liberate hydrogen gas and form borates.

5. Those substances can be separated by steam distillation which are:

• (a) steam volatile and insoluble in water
• (b) steam volatile and soluble in water
• (c) steam volatile and sparingly soluble in water
• (d) in liquid form in steam and solid form in water.

Correct Answer: (a)

Explanation: Steam distillation is used for substances that are volatile in steam but immiscible (insoluble) in water.

6. Reactivity of borazole is greater than that of benzene because:

• (a) borazole is polar compound
• (b) borazole is non-polar compound
• (c) borazole is electron-deficient compound
• (d) of localized electrons in it.

Correct Answer: (d)

Explanation: Unlike benzene where electrons are completely delocalised, in borazole ($B_{3}N_{3}H_{6}$), the electrons are relatively localised due to the electronegativity difference between B and N, making it more reactive.

7. Compounds of alkaline earth metals are less soluble in water than the corresponding alkali metals salts due to:

• (a) their high ionisaiton energy
• (b) their low electronegativity
• (c) their low hydration energy
• (d) their high lattice energy.

Correct Answer: (d)

Explanation: Due to their higher charge and smaller size, alkaline earth metal ions form lattices with much higher lattice energies, which often makes them less soluble.

8. The characteristic colour of the flame for caesium (Cs) is:

• (a) yellow
• (b) blue
• (c) lilac
• (d) red-violet.

Correct Answer: (b)

Explanation: Caesium imparts a characteristic blue colour to the flame.

9. Which of the following will not give Friedel-Craft's reaction in presence of anhydrous $AlCl_{3}$?

• (a) [Toluene]
• (b) [Benzyl chloride]
• (c) [Phenol]
• (d) [Aniline]

Correct Answer: (d)

Explanation: Aniline's $-NH_{2}$ group is strongly basic and reacts with the Lewis acid $AlCl_{3}$ to form a salt. This deactivates the benzene ring for electrophilic substitution.

10. Out of Si, Ge, Sn and Pb which forms stable ionic compounds in divalent state?

• (a) Pb
• (b) Sn
• (c) Ge
• (d) Si

Correct Answer: (a)

Explanation: Due to the inert pair effect, the +2 oxidation state becomes more stable than the +4 state as we move down the group. Lead (Pb) primarily forms stable ionic +2 compounds.

11. Aluminium metal is corroded in coastal places near to the sea because:

• (a) protective oxide film is removed by sea water
• (b) reacts with sea water
• (c) is attacked by salt present in sea water
• (d) reacts with sand particles.

Correct Answer: (c)

Explanation: The protective oxide layer on aluminium is penetrated and attacked by chloride ions from the salt in sea water, leading to corrosion.

12. In which of the following, the order is not strictly according to the property written against it?

• (a) $B < Al > Ga < In < Tl$ (Atomic radii)
• (b) $B > Al > Ga > In > Tl$ (Ionisation enthalpy)
• (c) $C > Si > Ge > Sn < Pb$ (Ionisation enthalpy)
• (d) $C > Si > Ge \approx Sn > Pb$ (Catenation)

Correct Answer: (b)

Explanation: The ionisation enthalpy in Group 13 does not decrease regularly. For example, $Tl$ has a higher IE than $In$ due to the inert pair effect and poor shielding of 4f electrons.

13. Match List I with List II (Detection/Method vs Reagent/Product):

• (P) Detect phosphorus: 4. $(NH_{4})_{2}MoO_{4}$
• (Q) Blood red colour in Lassaigne: 1. $[Fe(SCN)]Cl_{2}$
• (R) Dumas method: 2. $N_{2}$ gas
• (S) Kjeldahl's method: 3. $(NH_{4})_{2}SO_{4}$

Correct Answer: (b)

Explanation: Phosphorus is detected using ammonium molybdate (P-4). Blood red colour is due to ferric thiocyanate (Q-1). Dumas method estimates nitrogen as $N_{2}$ (R-2). Kjeldahl's involves ammonium sulphate (S-3).

14. Arrange the following carbanions in decreasing order of stability: $CH_{3}^{-}$ (I), $CH_{3}O^{-}$ (II), $CN^{-}$ (III), $NO_{2}^{-}$ (IV).

• (a) $I > III > IV$
• (b) $III > IV > II > I$
• (c) $IV > III > II > I$
• (d) $II > III > IV$

Correct Answer: (c)

Explanation: Electron-withdrawing groups (EWG) stabilise carbanions. The $-NO_{2}$ group is the strongest EWG, followed by $-CN$. Oxygen is more electronegative than carbon, so $CH_{3}O^{-}$ is more stable than $CH_{3}^{-}$.

15. Which statement is correct based on the fact that water freezes at 0°C and boils at 100°C?

• (a) Water dissolves anything however sparingly.
• (b) Water is a polar molecule.
• (c) Boiling and freezing temperatures of water were used to define a temperature scale.
• (d) Liquid water is denser than ice.

Correct Answer: (c)

Explanation: The Celsius scale was originally defined using the freezing and boiling points of water as fixed reference points (0°C and 100°C).

16. In the given conformation, if $C_{2}$ is rotated about $C_{2}-C_{3}$ bond anticlockwise by 120°, the conformation obtained is:

• (a) fully eclipsed
• (b) partially eclipsed
• (c) Gauche conformation
• (d) staggered.

Correct Answer: (c)

Explanation: Rotating a staggered form by 120° results in another staggered conformation, specifically a Gauche (skew) form where groups are at a 60° dihedral angle.

17. Which property shows that hydrogen resembles alkali metals?

• (a) It shows metallic character.
• (b) It is diatomic.
• (c) Its IE is of the same order as alkali metals.
• (d) During electrolysis, it is liberated at the cathode.

Correct Answer: (d)

Explanation: Like alkali metals, hydrogen is liberated at the cathode when its compounds (acids/salts) are electrolysed.

18. Identify Z in: $\text{2-propanol} \xrightarrow{conc. H_{2}SO_{4}} X \xrightarrow{Br_{2}} Y \xrightarrow{exc. alc. KOH} Z$

• (a) [structure a]
• (b) [structure b]
• (c) [structure c]
• (d) $CH_{3}-C \equiv CH$

Correct Answer: (d)

Explanation: 2-propanol dehydrates to propene (X). Propene reacts with $Br_{2}$ to give 1,2-dibromopropane (Y). Dehydrobromination with excess alc. KOH yields propyne (Z).

19. Positive soil pollution is:

• (a) reduction in productivity due to pesticides/fertilizers
• (b) reduction in productivity due to erosion
• (c) converting land to barren land by dumping garbage
• (d) none of these.

Correct Answer: (a)

Explanation: Positive soil pollution involves the addition of harmful substances like chemical fertilizers and pesticides that reduce soil quality.

20. An alkane has a C/H ratio (by mass) of 5.1428. Its molecular formula is:

• (a) $C_{7}H_{16}$
• (b) $C_{5}H_{12}$
• (c) $C_{6}H_{14}$
• (d) $C_{8}H_{18}$

Correct Answer: (c)

Explanation: For $C_{n}H_{2n+2}$, the mass ratio is $12n / (2n+2)$. For $n=6$, $72 / 14 \approx 5.1428$.

21. Which of the following is a false statement?

• (a) Free radicals are reaction intermediates.
• (b) Methane/Chlorine reaction proceeds via free radical.
• (c) Electronegative atom in a chain produces +I effect.
• (d) Homolytic fission gives free radicals.

Correct Answer: (c)

Explanation: Electronegative atoms pull electron density away, producing a -I (inductive withdrawal) effect, not +I.

22. The two strong acids present in acid rain are:

• (a) $HNO_{2}$ and $HNO_{3}$
• (b) $H_{2}SO_{4}$ and $HNO_{3}$
• (c) $H_{2}SO_{3}$ and $H_{2}SO_{4}$
• (d) $H_{2}CO_{3}$ and $HCl$

Correct Answer: (b)

Explanation: Acid rain is primarily composed of sulphuric acid and nitric acid formed from atmospheric pollutants.

23. Which one of the following is not a characteristic property of carbon?

• (a) It exhibits catenation.
• (b) It forms multiple bonds.
• (c) Its MP and BP are exceptionally high.
• (d) It shows semi-metallic character.

Correct Answer: (d)

Explanation: Carbon is a non-metal, whereas semi-metallic (metalloid) character begins later in the group with Silicon and Germanium.

24. $BF_{3}$ is the least acidic in the series $BF_{3}, BCl_{3}, BBr_{3}$ because:

• (a) F is most electronegative
• (b) F has small size
• (c) $B^{3+}$ has very small size
• (d) back donation of electrons from F to B occurs.

Correct Answer: (d)

Explanation: Strong $p\pi-p\pi$ back-bonding from Fluorine to Boron reduces the electron deficiency of the B atom, making $BF_{3}$ a weaker Lewis acid than its heavier analogues.

25. Chemical A removes temporary hardness, reacts with $Na_{2}CO_{3}$ to generate caustic soda, and turns cloudy with $CO_{2}$. A is:

• (a) $CaCO_{3}$
• (b) $CaO$
• (c) $Ca(OH)_{2}$
• (d) $Ca(HCO_{3})_{2}$

Correct Answer: (c)

Explanation: Slaked lime, $Ca(OH)_{2}$, is used in Clarke's process. It reacts with $Na_{2}CO_{3}$ to form $NaOH$ and $CaCO_{3}$ (caustisizing) and reacts with $CO_{2}$ to form a milky precipitate of $CaCO_{3}$.

26. Which of the following has the highest melting point?

• (a) 3-methyl-1-butene
• (b) 2-methyl-2-butene
• (c) 2,3-dimethyl-2-butene
• (d) 1-pentene.

Correct Answer: (c)

Explanation: Symmetrical and highly substituted alkenes like 2,3-dimethyl-2-butene have higher melting points due to better crystal lattice packing.

27. Water is often treated with chlorine to:

• (a) increase oxygen content
• (b) kill germs
• (c) remove suspended particles
• (d) remove hardness.

Correct Answer: (b)

Explanation: Chlorination is used as a disinfection stage in water treatment to kill pathogens and germs.

28. Permanent hardness of water is due to the presence of:

• (a) bicarbonates of Na/K
• (b) chlorides/sulphates of Na/K
• (c) chlorides/sulphates of Ca/Mg
• (d) bicarbonates of Ca/Mg.

Correct Answer: (c)

Explanation: Permanent hardness is caused by the chlorides and sulphates of Calcium and Magnesium ions.

29. The increasing order of density of alkali metals is:

• (a) $Li < K < Na < Rb < Cs$
• (b) $Li < Na < K < Rb < Cs$
• (c) $Cs < Rb < Na < K < Li$
• (d) $Cs < Rb < K < Na < Li$

Correct Answer: (a)

Explanation: Density generally increases down the group, but Potassium is lighter than Sodium due to an anomalous increase in atomic volume.

30. Which of the following is an incorrect statement?

• (a) $Tl^{3+}$ salts are better oxidising agents.
• (b) $Ga^{+}$ salts are better reducing agents.
• (c) $Pb^{4+}$ salts are better oxidising agents.
• (d) $As^{5+}$ salts are better oxidising agents.

Correct Answer: (d)

Explanation: According to the inert pair effect, the stability of higher oxidation states decreases down the group. $As^{5+}$ is stable and not a strong oxidant like $Bi^{5+}$.

31. An alkene that produces 2 moles of propanone upon ozonolysis is:

• (a) 3-methyl-1-butene
• (b) 2,3-dimethyl-1-butene
• (c) 2,3-dimethyl-2-pentene
• (d) 2,3-dimethyl-2-butene.

Correct Answer: (d)

Explanation: Ozonolysis of 2,3-dimethyl-2-butene ($(CH_{3})_{2}C=C(CH_{3})_{2}$) cleaves the double bond to yield two molecules of acetone (propanone).

32. Benzene easily shows:

• (a) ring fission
• (b) addition reactions
• (c) electrophilic substitution
• (d) nucleophilic substitution.

Correct Answer: (c)

Explanation: Benzene prefers electrophilic substitution reactions because they allow the ring to retain its stable aromatic system.

33. Cis-2-butene and trans-2-butene are:

• (a) conformational isomers
• (b) structural isomers
• (c) configurational isomers
• (d) optical isomers.

Correct Answer: (c)

Explanation: Geometrical isomers are a type of configurational isomers because they cannot be interconverted without breaking bonds.

34. Nature of Si-O bond in silicates:

• (a) purely ionic
• (b) purely covalent
• (c) metallic
• (d) 50% covalent and 50% ionic.

Correct Answer: (d)

Explanation: Based on the electronegativity difference between Silicon and Oxygen, the bond is estimated to be approximately half covalent and half ionic.

35. Heavy water is manufactured by:

• (a) combination of H and heavy O
• (b) electrolysis of water with dissolved heavy H
• (c) repeated electrolysis of 3% NaOH solution
• (d) none of these.

Correct Answer: (c)

Explanation: Heavy water ($D_{2}O$) is obtained by the prolonged electrolysis of ordinary water containing an electrolyte like sodium hydroxide.

36. Stability of conformations of cyclohexane decreases in order:

• (a) chair > half chair > boat > twist boat
• (b) chair > twist boat > boat > half chair
• (c) chair > boat > twist boat > half chair
• (d) boat > twist boat > chair > half chair

Correct Answer: (b)

Explanation: The chair form is most stable. The twist-boat is more stable than the boat due to less flag-pole repulsion, and the half-chair is the least stable.

37. Which element does not form hydride by direct heating with hydrogen?

• (a) Be
• (b) Mg
• (c) Sr
• (d) Ba

Correct Answer: (a)

Explanation: Beryllium does not react directly with hydrogen; its hydride is prepared by other methods like reduction of $BeCl_{2}$.

38. Which of the following statements about alkali metals is correct?

• 1. $Cs^{+}$ is more highly hydrated than others.
• 2. Lithium has the highest melting point.
• 3. Only Lithium forms a stable nitride directly.

Correct Answer: (d)

Explanation: Statements 2 and 3 are correct. Lithium has the highest MP and is the only alkali metal to form a nitride ($Li_{3}N$) directly. Statement 1 is false as $Li^{+}$ is the most highly hydrated due to its small size.

39. Which of the following is not a meta-directing group?

• (a) $-NH_{3}^{+}$
• (b) $-CF_{3}$
• (c) $-Br$
• (d) $-SO_{3}H$

Correct Answer: (c)

Explanation: Halogens like Bromine are deactivating but ortho/para directing due to resonance (+R effect).

40. Correct representation of 3-methylpent-3-en-2-ol is:

• (a) [structure a]
• (b) [structure b]
• (c) [structure c]
• (d) [structure d]

Correct Answer: (a)

Explanation: Based on IUPAC numbering, the 5-carbon chain has an -OH at C2, a double bond starting at C3, and a methyl group at C3.

41. General formula of a ring or cyclic silicate is:

• (a) $(Si_{2}O_{5})_{n}^{2n-}$
• (b) $(SiO_{3})_{n}^{2n-}$
• (c) $(SiO_{3}^{2-})_{n}$
• (d) both (b) and (c).

Correct Answer: (d)

Explanation: Cyclic silicates are formed by sharing two oxygen atoms per tetrahedron, leading to the formula $(SiO_{3})_{n}^{2n-}$.

42. Aluminium hydroxide is soluble in excess NaOH forming the ion:

• (a) $AlO_{2}^{3+}$
• (b) $AlO_{2}^{-}$
• (c) $AlO_{2}^{3-}$
• (d) $AlO_{3}^{-}$

Correct Answer: (b)

Explanation: $Al(OH)_{3}$ is amphoteric and dissolves in excess base to form the soluble meta-aluminate ion ($AlO_{2}^{-}$).

43. Which of the following statements is not correct?

• (a) Pure para-H is obtained by cooling to 20K.
• (b) Ortho/Para ratio at 300K is 3:1.
• (c) Ratio varies with temperature.
• (d) Pure ortho-H is obtained by heating above 300K.

Correct Answer: (d)

Explanation: While the ratio changes with temperature, it is not possible to obtain 100% ortho-hydrogen by heating.

44. In the given reactions, which of the following is not correct?

• (a) $2Li_{2}O \xrightarrow{\Delta} Li_{2}O_{2} + Li$
• (b) $2K_{2}O \xrightarrow{\Delta} K_{2}O_{2} + 2K$
• (c) $2Na_{2}O \xrightarrow{\Delta} Na_{2}O_{2} + 2Na$
• (d) $2Rb_{2}O \xrightarrow{\Delta} Rb_{2}O_{2} + 2Rb$

Correct Answer: (a)

Explanation: Lithium oxide is exceptionally stable due to its high lattice energy and does not decompose in this manner; Lithium prefers the oxide form.

45. What is true about DDT?

• (a) Biodegradable pollutant
• (b) Greenhouse gas
• (c) Fertilizer
• (d) Non-biodegradable pollutant

Correct Answer: (d)

Explanation: DDT is a persistent, non-biodegradable pollutant that accumulates in the food chain.