The p-Block Elements (Group 15 to 18) - MCQs with Explanations

1. How many lone pair of electrons are present on Xe in \(XeOF_{4}\)?

• (a) 1
• (b) 2
• (c) 3
• (d) 4

Correct Answer: (a)

Explanation: Xe in \(XeOF_{4}\) has \(sp^{3}d^{2}\) hybridisation with one lone pair of electron.

2. Which acid has P - P linkage?

• (a) Hypophosphoric acid
• (b) Pyrophosphoric acid
• (c) Metaphosphoric acid
• (d) Orthophosphoric acid

Correct Answer: (a)

Explanation: Hypophosphoric acid (\(H_{4}P_{2}O_{6}\)) is \(HO-P-P-OH\) with two \(P=O\) and two \(OH\) groups on each P, containing a direct P-P bond.

3. In the manufacture of \(H_{2}SO_{4}\) the nitrated acid from the Gay-Lussac's tower is chemically:

• (a) \(H_{2}SO_{4}\cdot NO_{2}\)
• (b) \(H_{2}SO_{4}\cdot NO\)
• (c) \(H_{2}SO_{4}\cdot 2NO\)
• (d) \(HSO_{4}\cdot NO\)

Correct Answer: (d)

Explanation: The reaction is \(2H_{2}SO_{4} + NO + NO_{2} \rightarrow 2NO\cdot HSO_{4} + H_{2}O\).

4. Arrange the acids (I) \(H_{2}SO_{4}\), (II) \(H_{3}PO_{3}\), and (III) \(HClO_{3}\) in the decreasing order of acidity.

• (a) \(I > III > II\)
• (b) \(I > II > III\)
• (c) \(III > II\)
• (d) \(II > III > I\)

Correct Answer: (a)

Explanation: Acidity increases with the electronegativity and oxidation state of the central atom. \(H_{2}SO_{4}\) (+6) is strongest, followed by \(HClO_{3}\) (+5), then \(H_{3}PO_{3}\) (+3).

5. Coconut charcoal at \(-180^{\circ}C\) is used to separate a mixture of:

• (a) Ar and Kr
• (b) Ne and Ar
• (c) Ne and Kr
• (d) He and Ne

Correct Answer: (d)

Explanation: Adsorption on coconut charcoal is used to separate noble gases based on their varying degrees of adsorption at low temperatures.

6. Identify the incorrect statement among the following.

• (a) Ozone reacts with \(SO_{2}\) to give \(SO_{3}\).
• (b) Silicon reacts with \(NaOH_{(aq)}\) in the presence of air to give \(Na_{2}SiO_{3}\) and \(H_{2}O\).
• (c) \(Cl_{2}\) reacts with excess of \(NH_{3}\) to give \(N_{2}\) and \(NH_{4}Cl\).
• (d) \(Br_{2}\) reacts with hot and strong NaOH solution to give \(NaBr\), \(NaBrO_{3}\) and \(H_{2}O\).

Correct Answer: (b)

Explanation: Silicon reacts with aqueous NaOH to produce sodium silicate and hydrogen gas, not water.

7. Which of the following represents the isopolyacid of phosphorus?

• (a) \(H-P-O-P-OH\) structure
• (b) \(H-P-P-OH\) structure
• (c) \(H-P-O-P-H\) structure
• (d) \(HO-P-O-P-OH\) structure (\(H_{4}P_{2}O_{7}\))

Correct Answer: (d)

Explanation: Pyrophosphoric acid (\(H_{4}P_{2}O_{7}\)) is a tetrabasic acid where each phosphorus atom lies in the same tetrahedral environment.

8. In the reaction, \(2Br^{-} + X_{2} \rightarrow Br_{2} + 2X^{-}\); \(X_{2}\) is:

• (a) \(Cl_{2}\)
• (b) \(Br_{2}\)
• (c) \(I_{2}\)
• (d) \(N_{2}\)

Correct Answer: (a)

Explanation: Chlorine (\(Cl_{2}\)) is a stronger oxidizing agent than bromine and can displace it from bromide solutions.

9. Sea divers go deep in the sea water with a mixture of which of the following gases?

• (a) \(O_{2}\) and He
• (b) \(O_{2}\) and Ar
• (c) \(O_{2}\) and \(CO_{2}\)
• (d) \(CO_{2}\) and Ar

Correct Answer: (a)

Explanation: Helium is used with oxygen because it has very low solubility in blood even at high pressures.

10. Which of the following statements is false regarding the \(SO_{3}\) molecule?

• (a) Sulphur can expand its octet to reduce formal charges.
• (b) The S-O bond is polar.
• (c) The O-S-O bond angle is \(104^{\circ}\).
• (d) It is a non-polar molecule.

Correct Answer: (c)

Explanation: \(SO_{3}\) has a trigonal planar shape with O-S-O bond angles of \(120^{\circ}\).

11. The compound iodine monofluoride (IF) would dissolve best in:

• (a) octane
• (b) carbon disulphide
• (c) benzene
• (d) methanol

Correct Answer: (d)

Explanation: IF is a polar molecule due to the difference in electronegativity and dissolves best in polar solvents like methanol.

12. Match the list I with list II and select the correct answer.

P. Tribasic acid; Q. Dibasic acid; R. Acid hydride of nitrogen; S. Basic hydride of nitrogen.

• (a) P-1, Q-2, R-3, S-4
• (b) P-3, Q-4, R-1, S-2
• (c) P-4, Q-2, R-1, S-3
• (d) P-2, Q-3, R-1, S-4

Correct Answer: (c)

Explanation: Orthophosphoric acid is tribasic (4); Orthophosphorous acid is dibasic (2); Hydrazoic acid is an acid hydride (1); Ammonia is a basic hydride (3).

13. Which of the following has maximum number of lone pairs associated with Xe?

• (a) \(XeF_{4}\)
• (b) \(XeF_{6}\)
• (c) \(XeF_{2}\)
• (d) \(XeO_{3}\)

Correct Answer: (c)

Explanation: \(XeF_{2}\) has 3 lone pairs of electrons on the xenon atom.

14. Which of the following statements is not true?

• (a) Halogens act as strong oxidizing agents.
• (b) Fluorine oxidizes water to oxygen and ozone.
• (c) Iodine has good solubility in water.
• (d) Solubility of iodine increases by adding KI.

Correct Answer: (c)

Explanation: Iodine has very poor solubility in water; it does not decompose water.

15. Which has maximum number of oxo groups (\(M=O\))?

• (a) \(H_{2}SO_{4}\)
• (b) \(H_{2}SO_{3}\)
• (c) \(H_{3}PO_{3}\)
• (d) \(H_{3}PO_{4}\)

Correct Answer: (a)

Explanation: \(H_{2}SO_{4}\) has 2 oxo (\(S=O\)) groups, while the others have 1.

16. Which of the following statements is correct?

• (a) \(SF_{6}\) does not react with water.
• (b) \(SF_{6}\) is \(sp^{3}d\) hybridized.
• (c) \(S_{2}O_{3}^{2-}\) is a linear ion.
• (d) There is no \(\pi\)-bonding in \(SO_{4}^{2-}\).

Correct Answer: (a)

Explanation: \(SF_{6}\) is chemically inert and does not undergo hydrolysis due to steric hindrance.

17. In solid state, \(PCl_{5}\) exists as:

• (a) \([PCl_{4}]^{-}\) and \([PCl_{7}]^{+}\) ions
• (b) covalent \(PCl_{5}\) molecules
• (c) \([PCl_{4}]^{+}\) and \([PCl_{6}]^{-}\) ions
• (d) \([PCl_{3}]^{2-}\) and \([PCl_{5}]^{2+}\) ions

Correct Answer: (c)

Explanation: Solid \(PCl_{5}\) is an ionic compound composed of tetrahedral \([PCl_{4}]^{+}\) and octahedral \([PCl_{6}]^{-}\) ions.

18. Match List I with List II (Xenon compound shapes).

P. \(XeF_{4}\); Q. \(XeF_{6}\); R. \(XeO_{3}\); S. \(XeO_{4}\).

• (a) P-3, Q-1, R-4, S-2
• (b) P-4, Q-2, R-1, S-3
• (c) P-1, Q-3, R-2, S-4
• (d) P-2, Q-4, R-3, S-1

Correct Answer: (a)

Explanation: \(XeF_{4}\) is square planar (3); \(XeF_{6}\) is distorted octahedral (1); \(XeO_{3}\) is pyramidal (4); \(XeO_{4}\) is tetrahedral (2).

19. Which of the xenon fluorides is isostructural with \(ICl_{4}^{-}\)?

• (a) \(XeF_{6}\)
• (b) \(XeF_{4}\)
• (c) \(XeF_{2}\)
• (d) \(XeF_{8}^{2-}\)

Correct Answer: (b)

Explanation: Both \(XeF_{4}\) and \(ICl_{4}^{-}\) have square planar geometry.

20. \(XeF_{4}\) reacts violently with water to give:

• (a) \(Xe + O_{2}\)
• (b) \(XeO_{3} + O_{2} + HF\)
• (c) \(Xe + F_{2} + H_{2}F_{2} + XeO_{3}\)
• (d) \(XeOF_{3}\)

Correct Answer: (b)

Explanation: Violent hydrolysis of \(XeF_{4}\) yields \(XeO_{3}\) along with \(O_{2}\) and \(HF\).

21. \(XeF_{4}\) exists whereas \(XeCl_{4}\) is not stable because:

• (a) electron affinity of Cl > F
• (b) oxidation potential of F > Cl
• (c) size of F is smaller than Cl
• (d) none of the above

Correct Answer: (c)

Explanation: The smaller size of Fluorine allows it to stabilize high oxidation states of Xenon better than Chlorine.

22. Chlorine is often added as the last step in municipal water treatment. The reason is:

• (a) in water, it forms HCl and HOCl (oxidising agent) which kill pathogens
• (b) it deters theft due to its history as a toxic gas
• (c) it is a reducing agent
• (d) it promotes growth of beneficial fungi

Correct Answer: (a)

Explanation: Chlorine reacts with water to form hypochlorous acid (\(HOCl\)), which is a powerful oxidant that kills bacteria and viruses.

23. Elements of group 16 are called chalcogens because:

• (a) they are present in many metallic ores as oxides and sulphides
• (b) many acids contain these elements
• (c) they mainly form anions
• (d) they exist in different allotropic forms

Correct Answer: (a)

Explanation: The term "chalcogen" refers to ore-forming elements, as most minerals are oxides or sulphides.

24. Which sequence represents the correct increasing order of bond angles?

• (a) \(H_{2}O < OF_{2} < OCl_{2} < ClO_{2}\)
• (b) \(OCl_{2} < ClO_{2} < H_{2}O < OF_{2}\)
• (c) \(OF_{2} < H_{2}O < OCl_{2} < ClO_{2}\)
• (d) \(ClO_{2} < OF_{2} < OCl_{2} < H_{2}O\)

Correct Answer: (c)

Explanation: Bond angles follow the order: \(OF_{2}\) (\(103^{\circ}\)) < \(H_{2}O\) (\(104.5^{\circ}\)) < \(OCl_{2}\) (\(111^{\circ}\)) < \(ClO_{2}\) (\(118^{\circ}\)).

25. Which of the following is the life saving mixture for an asthma patient?

• (a) Mixture of helium and oxygen
• (b) Mixture of neon and oxygen
• (c) Mixture of xenon and nitrogen
• (d) Mixture of argon and oxygen

Correct Answer: (a)

Explanation: A mixture of Helium and Oxygen (\(1:4\)) is used for patients with respiratory distress like asthma because it is easier to breathe.

26. There is very little difference in acid strength in the series \(H_{3}PO_{3}\) and \(H_{3}PO_{2}\) because:

• (a) P exists in different oxidation states
• (b) number of unprotonated oxygen atoms remains the same
• (c) phosphorus is not highly electronegative
• (d) phosphorus oxides are less basic

Correct Answer: (b)

Explanation: Both acids have one non-hydrogen bonded (oxo) oxygen, which primarily determines the acid strength through inductive effect.

27. Which of the following correctly describes the tetrathionate ion (\(S_{4}O_{6}^{2-}\)) structure?

• (a) Two S-atoms have +5 state, two have 0
• (b) All S-atoms are equivalent
• (c) It contains S-O-O-S linkage
• (d) It contains cyclic structure

Correct Answer: (a)

Explanation: In tetrathionate ion, the two central S-atoms have an oxidation state of 0, while the terminal S-atoms are in the +5 state.

28. In spite of being an odd-electron molecule \(ClO_{2}\) does not dimerize because:

• (a) the odd electron is delocalized
• (b) the odd electron is localized on Cl
• (c) Cl-O bond lengths are different
• (d) of \(p\pi-p\pi\) bonding in chlorine

Correct Answer: (a)

Explanation: The delocalization of the odd electron over the molecule reduces the tendency for dimerization.

29. Oxidation states of P in \(H_{4}P_{2}O_{5}\), \(H_{4}P_{2}O_{6}\) and \(H_{4}P_{2}O_{7}\) are respectively:

• (a) +3, +5, +4
• (b) +5, +3, +4
• (c) +5, +4, +3
• (d) +3, +4, +5

Correct Answer: (d)

Explanation: These correspond to Pyrophosphorous (+3), Hypophosphoric (+4), and Pyrophosphoric (+5) acids.

30. The correct order of increasing bond angles in the following species is:

• (a) \(Cl_{2}O < ClO_{2} < ClO_{2}^{-}\)
• (b) \(ClO_{2} < Cl_{2}O < ClO_{2}^{-}\)
• (c) \(Cl_{2}O < ClO_{2}^{-} < ClO_{2}\)
• (d) \(ClO_{2}^{-} < Cl_{2}O < ClO_{2}\)

Correct Answer: (d)

Explanation: Due to varying electron-electron repulsions and hybridization, the order is \(ClO_{2}^{-} < Cl_{2}O < ClO_{2}\).

31. In pyrophosphoric acid (\(H_{4}P_{2}O_{7}\)), number of \(\sigma\) and \(d\pi-p\pi\) bonds respectively are:

• (a) 8 and 2
• (b) 6 and 2
• (c) 12 and zero
• (d) 12 and 2

Correct Answer: (d)

Explanation: The structure contains 12 sigma bonds and 2 \(d\pi-p\pi\) bonds (the two \(P=O\) double bonds).

32. The increasing order of volatility of hydrides of group 16 elements is:

• (a) \(H_{2}S < H_{2}O < H_{2}Se < H_{2}Te\)
• (b) \(H_{2}O < H_{2}Te < H_{2}Se < H_{2}S\)
• (c) \(H_{2}O < H_{2}S < H_{2}Se < H_{2}Te\)
• (d) \(H_{2}Te < H_{2}Se < H_{2}S < H_{2}O\)

Correct Answer: (b)

Explanation: \(H_{2}O\) is least volatile due to hydrogen bonding. For others, volatility decreases with increasing molecular weight.

33. Which statement regarding the manufacture of \(H_{2}SO_{4}\) by contact process is false?

• (a) Sulphur is burnt in air to form \(SO_{2}\).
• (b) \(SO_{2}\) is catalytically oxidised to \(SO_{3}\).
• (c) \(SO_{3}\) is dissolved in water to get 100% sulphuric acid.
• (d) Contact process produces acid of higher purity.

Correct Answer: (c)

Explanation: In the contact process, \(SO_{3}\) is dissolved in concentrated \(H_{2}SO_{4}\) to form oleum, which is then diluted; dissolving it directly in water produces a difficult-to-condense fog.

34. \(PCl_{5}\) exists but \(NCl_{5}\) does not because:

• (a) nitrogen has no vacant d-orbitals
• (b) \(NCl_{5}\) is unstable
• (c) nitrogen atom is smaller
• (d) nitrogen is highly inert

Correct Answer: (a)

Explanation: Nitrogen, being in the second period, lacks the d-orbitals necessary to expand its octet and form five bonds.

35. Fluorine molecule is formed by:

• (a) axial p-p orbital overlap
• (b) sideways p-p orbital overlap
• (c) s-s orbital overlap
• (d) s-p overlap

Correct Answer: (a)

Explanation: The single sigma bond in \(F_{2}\) is formed by the head-on (axial) overlap of two p-orbitals.

36. Iodine is more soluble in alcohol than in carbon tetrachloride because:

• (a) iodine and alcohol both are non-polar
• (b) randomness is greater in alcohol
• (c) dissolution in alcohol is exothermic
• (d) heat of dissolution in alcohol is less than in \(CCl_{4}\)

Correct Answer: (d)

Explanation: Solubility is higher when the endothermic heat of dissolution is lower, as energy is a major opposing factor.

37. When \(SO_{2}\) is passed through acidified \(K_{2}Cr_{2}O_{7}\) solution:

• (a) the solution turns blue
• (b) the solution is decolourised
• (c) \(SO_{2}\) is reduced
• (d) green \(Cr_{2}(SO_{4})_{3}\) is formed

Correct Answer: (d)

Explanation: Chromium is reduced from +6 (orange) to +3 (green) to form chromium sulphate.

38. Which one of the following is pyrophosphoric acid?

• (a) \(H_{3}PO_{4}\)
• (b) \(H_{4}P_{2}O_{7}\)
• (c) \(H_{4}P_{2}O_{5}\)
• (d) \(H_{3}PO_{4}\)

Correct Answer: (b)

Explanation: Pyrophosphoric acid is formed by the condensation of two molecules of orthophosphoric acid.

39. Oxygen is gas but sulphur is solid because:

• (a) oxygen has discrete molecules while sulphur is polymeric
• (b) molecular weight of sulphur is much higher
• (c) oxygen is a stronger oxidizing agent
• (d) boiling point of sulphur is higher

Correct Answer: (a)

Explanation: Oxygen forms diatomic molecules (\(O_{2}\)), while sulphur forms stable octatomic rings (\(S_{8}\)) or chains.

40. Which statement is correct about halogens?

• (a) They are all diatomic and form univalent ions.
• (b) They are all capable of exhibiting several oxidation states.
• (c) They are all diatomic and form divalent ions.
• (d) They can mutually displace each other from solutions.

Correct Answer: (a)

Explanation: All halogens exist as \(X_{2}\) molecules and tend to gain one electron to form \(X^{-}\) ions.

41. The structure of \(IF_{7}\) is:

• (a) square pyramid
• (b) trigonal bipyramid
• (c) octahedral
• (d) pentagonal bipyramid

Correct Answer: (d)

Explanation: \(IF_{7}\) has \(sp^{3}d^{3}\) hybridization, resulting in a pentagonal bipyramidal geometry.

42. In the reaction \(HNO_{3} + P_{2}O_{5} \rightarrow A + B\), A and B are:

• (a) \(H_{3}PO_{4}, N_{2}O_{3}\)
• (b) \(HPO_{3}, N_{2}O_{3}\)
• (c) \(HPO_{3}, N_{2}O_{5}\)
• (d) \(H_{3}PO_{3}, N_{2}O_{5}\)

Correct Answer: (c)

Explanation: Phosphorus pentoxide dehydrates nitric acid to form nitrogen pentoxide and metaphosphoric acid.

43. Which of the following is correct regarding basic character?

• (a) \(H_{2}Te > H_{2}Se > H_{2}S < H_{2}O\)
• (b) \(NH_{3} > PH_{3} > AsH_{3} > SbH_{3}\)
• (c) \(HF < HBr < HI < HCl\)
• (d) \(F_{2} > Cl_{2} > Br_{2} > I_{2}\)

Correct Answer: (b)

Explanation: Basicity decreases down the group due to increasing size and decreasing electron density of the lone pair.

44. The increase in boiling points of the noble gases from He to Xe is due to:

• (a) decrease in ionization enthalpy
• (b) increase in polarization
• (c) increase in atomic volume
• (d) increase in electron gain enthalpy

Correct Answer: (b)

Explanation: As size increases, polarizability increases, leading to stronger van der Waals forces and higher boiling points.

45. Which of the following shapes is NOT exhibited by \(SO_{2}\), \(SF_{4}\), \(ClF_{3}\), \(BrF_{5}\), or \(XeF_{4}\)?

• (a) Bent
• (b) Trigonal bipyramidal
• (c) See-saw
• (d) T-shape

Correct Answer: (b)

Explanation: \(SO_{2}\) is bent; \(SF_{4}\) is see-saw; \(ClF_{3}\) is T-shape; \(BrF_{5}\) is square pyramidal; \(XeF_{4}\) is square planar. None are purely trigonal bipyramidal.