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p-Block Elements (Groups 15-18)

31 NEET-UG practice questions on p-Block Elements (Groups 15-18), part of Chemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

  1. Question 1 · Medium

    Given below are two statements: Statement I: The two O–O bonds in ozone have different lengths. Statement II: Ozone is thermodynamically unstable with respect to oxygen because its decomposition is exothermic and increases the entropy. Choose the correct answer.

    1. ABoth Statement I and Statement II are correct
    2. BStatement I is correct but Statement II is incorrect
    3. CBoth Statement I and Statement II are incorrect
    4. DStatement I is incorrect but Statement II is correct
    Show answer

    Answer: D · Statement I is incorrect but Statement II is correct

    Ozone is a resonance hybrid, so both O–O bonds have the same length of 128 pm, and Statement I is false. Its decomposition releases heat and raises the entropy, so ΔG is negative and Statement II is true.

    • A: Statement I is false; resonance makes the bonds equal.
    • B: The statements are reversed; I is false and II is true.
    • C: Statement II is true; decomposition of O₃ has a negative ΔG.

    Remember this

    Resonance makes the two O–O bonds equal, between a single and a double bond in length.

  2. Question 2 · Hard

    Complete hydrolysis of XeF₆ gives a xenon compound. Which option correctly names that compound and its shape?

    1. AXeOF₄, square pyramidal
    2. BXeO₃, pyramidal
    3. CXeO₂F₂, see-saw
    4. DXeO₃, trigonal planar
    Show answer

    Answer: B · XeO₃, pyramidal

    XeF₆ + 3H₂O → XeO₃ + 6HF. In XeO₃, xenon has three bond pairs and one lone pair on its sp³ arrangement, so the molecule is pyramidal.

    • A: XeOF₄ comes from partial hydrolysis.
    • C: XeO₂F₂ also comes from partial hydrolysis.
    • D: Right compound, but it ignores the lone pair on xenon.

    Remember this

    XeF₆ gives XeOF₄ then XeO₂F₂ on partial hydrolysis, and XeO₃ on complete hydrolysis.

  3. Question 3 · Hard

    On heating, phosphorous acid disproportionates: H₃PO₃ → H₃PO₄ + PH₃ (unbalanced). In the balanced reaction, what is the ratio of phosphorus atoms oxidised to those reduced?

    1. A1 : 3
    2. B2 : 1
    3. C1 : 1
    4. D3 : 1
    Show answer

    Answer: D · 3 : 1

    P goes from +3 to +5 in H₃PO₄ (loses 2 e⁻) and from +3 to −3 in PH₃ (gains 6 e⁻). Electron balance needs three oxidised per one reduced, so 4H₃PO₃ → 3H₃PO₄ + PH₃.

    • A: Inverts the ratio, mixing up oxidation and reduction.
    • B: Takes the change to PH₃ as 4 electrons rather than 6.
    • C: Assumes equal numbers without balancing electrons.

    Remember this

    In disproportionation, balance the electrons lost and gained; the oxidation-state changes set the ratio.

  4. Question 4 · Medium

    Arrange the steps of the contact process in the correct order. A. Diluting oleum with water B. Catalytic oxidation of SO₂ over V₂O₅ C. Burning sulphur or a sulphide ore to give SO₂ D. Absorbing SO₃ in concentrated H₂SO₄

    1. AC, B, D, A
    2. BC, B, A, D
    3. CB, C, D, A
    4. DC, D, B, A
    Show answer

    Answer: A · C, B, D, A

    SO₂ is produced first, then oxidised over V₂O₅ to SO₃. SO₃ is absorbed in sulphuric acid to give oleum, H₂S₂O₇, which is diluted to the required strength.

    • B: Dilutes oleum before it has been formed.
    • C: Oxidises SO₂ before it has been made.
    • D: Absorbs SO₃ before it has been made.

    Remember this

    SO₃ is not dissolved directly in water; it goes through oleum first.

  5. Question 5 · Medium

    Match List-I with List-II. List-I (interhalogen) A. ClF B. ClF₃ C. IF₅ D. IF₇ List-II (shape) I. Pentagonal bipyramidal II. Bent T-shaped III. Linear IV. Square pyramidal

    1. AA-III, B-II, C-I, D-IV
    2. BA-III, B-II, C-IV, D-I
    3. CA-III, B-IV, C-II, D-I
    4. DA-II, B-III, C-IV, D-I
    Show answer

    Answer: B · A-III, B-II, C-IV, D-I

    ClF is diatomic, so linear. ClF₃ has 3 bond pairs and 2 lone pairs (bent T), IF₅ has 5 and 1 (square pyramidal), and IF₇ has 7 and 0 (pentagonal bipyramidal).

    • A: Swaps the shapes of IF₅ and IF₇.
    • C: Swaps the shapes of ClF₃ and IF₅.
    • D: Swaps the shapes of ClF and ClF₃.

    Remember this

    Interhalogen shapes follow VSEPR from the bond and lone pairs on the central, larger halogen.

  6. Question 6 · Easy

    Copper reacts with dilute nitric acid. Identify the nitrogen-containing gas evolved.

    1. ANH₃
    2. BNO₂
    3. CN₂O
    4. DNO

    Answer and explanation in LearnFree account

  8. Question 8 · Medium

    Copper(II) sulphate solution is treated with excess aqueous ammonia and turns deep blue. Which species is responsible for this colour?

    1. ACu(OH)₂
    2. BCuO
    3. C[Cu(NH₃)₄]²⁺
    4. D[Cu(NH₃)₂]⁺

    Answer and explanation in LearnFree account

  9. Question 9 · Medium

    Chlorine gas is passed into hot, concentrated NaOH solution. Which chlorine-containing salts are formed?

    1. ANaCl and NaClO₃
    2. BNaClO₃ and NaClO₄
    3. CNaCl and NaOCl
    4. DNaOCl and NaClO₄

    Answer and explanation in LearnFree account

  12. Question 12 · Medium

    Phosphorus pentachloride is treated with a limited amount of water. Which products are formed?

    1. AH₃PO₃ and HCl
    2. BPCl₃ and HOCl
    3. CPOCl₃ and HCl
    4. DH₃PO₄ and HCl

    Answer and explanation in LearnFree account

  13. Question 13 · Medium

    Arrange the halogens in decreasing order of bond dissociation enthalpy. A. F₂ B. Cl₂ C. Br₂ D. I₂

    1. AA, B, C, D
    2. BD, C, B, A
    3. CB, A, C, D
    4. DB, C, A, D

    Answer and explanation in LearnFree account

  14. Question 14 · Hard

    Read these statements about oxoacids: A. Phosphorous acid, H₃PO₃, contains two P-H bonds. B. Pyrophosphoric acid, H₄P₂O₇, contains a P-O-P linkage. C. Peroxodisulphuric acid, H₂S₂O₈, contains an O-O linkage. D. Pyrosulphuric acid, H₂S₂O₇, contains an S-S bond. Which of them are correct?

    1. AB and C only
    2. BC and D only
    3. CB, C and D only
    4. DA, B and C only

    Answer and explanation in LearnFree account

  15. Question 15 · Medium

    Assertion A: Nitrogen forms NCl₃ but not NCl₅, whereas phosphorus forms both PCl₃ and PCl₅. Reason R: Nitrogen has no d orbitals in its valence shell, so it cannot expand its covalency beyond four. Choose the correct answer.

    1. AA is correct but R is not correct
    2. BBoth A and R are correct and R is the correct explanation of A
    3. CBoth A and R are correct but R is not the correct explanation of A
    4. DA is not correct but R is correct

    Answer and explanation in LearnFree account

  16. Question 16 · Hard

    White phosphorus is heated with concentrated NaOH solution in an inert atmosphere, giving a gas X. X is passed into copper sulphate solution, giving Y; X also combines with HI to give Z. Identify Y and Z.

    1. AY = Cu₃(PO₄)₂; Z = PH₄I
    2. BY = Cu₃P₂; Z = PI₃
    3. CY = Cu(H₂PO₂)₂; Z = PI₃
    4. DY = Cu₃P₂; Z = PH₄I

    Answer and explanation in LearnFree account

  17. Question 17 · Easy

    Arrange the oxoacids of chlorine in increasing order of acid strength. A. HClO₄ B. HOCl C. HClO₃ D. HClO₂

    1. AD, B, C, A
    2. BB, D, C, A
    3. CB, C, D, A
    4. DA, C, D, B

    Answer and explanation in LearnFree account

  18. Question 18 · Medium

    Match List-I with List-II. List-I (oxoacid) A. H₂S₂O₈ B. H₂SO₃ C. HClO₄ D. H₃PO₃ List-II (oxidation state of the central atom) I. +6 II. +3 III. +7 IV. +4 Choose the correct answer.

    1. AA-IV, B-I, C-III, D-II
    2. BA-I, B-IV, C-III, D-II
    3. CA-III, B-IV, C-I, D-II
    4. DA-I, B-II, C-III, D-IV

    Answer and explanation in LearnFree account

  19. Question 19 · Medium

    Chlorine reacts with ammonia in two ways depending on which reactant is in excess. Which option gives the products, first with excess ammonia and then with excess chlorine?

    1. AN₂ and NH₄Cl; NCl₃ and HCl
    2. BNH₂Cl and HCl; N₂ and HCl
    3. CN₂H₄ and HCl; NCl₃ and NH₄Cl
    4. DNCl₃ and HCl; N₂ and NH₄Cl

    Answer and explanation in LearnFree account

  20. Question 20 · Medium

    Given below are two statements: Statement I: The XeF₂ molecule is linear. Statement II: Interhalogen compounds are less reactive than the halogens (except fluorine) because the X–X′ bond is stronger than the X–X bond. Choose the correct answer.

    1. AStatement I is incorrect but Statement II is correct
    2. BBoth Statement I and Statement II are incorrect
    3. CBoth Statement I and Statement II are correct
    4. DStatement I is correct but Statement II is incorrect

    Answer and explanation in LearnFree account

  21. Question 21 · Medium

    Arrange the following hydrides in decreasing order of their H–M–H bond angle. A. PH₃ B. SbH₃ C. NH₃ D. AsH₃

    1. AC, A, D, B
    2. BC, D, A, B
    3. CA, C, D, B
    4. DB, D, A, C

    Answer and explanation in LearnFree account

  22. Question 22 · Medium

    Phosphorus pentoxide exists as P₄O₁₀. How many P–O–P bridging linkages are present in one P₄O₁₀ molecule?

    1. A4
    2. B5
    3. C6
    4. D10

    Answer and explanation in LearnFree account

  23. Question 23 · Hard

    Examine the following claims on sulphur and chlorine oxoacids. A. Pyrosulphuric acid (oleum), H₂S₂O₇, contains an S–O–S linkage. B. HClO₄ is a stronger acid than HClO. C. Peroxodisulphuric acid, H₂S₂O₈, contains an O–O linkage. D. Sulphur is in the +6 oxidation state in H₂SO₃. Which of them are correct?

    1. AA, B and D only
    2. BA, B and C only
    3. CA and C only
    4. DB, C and D only

    Answer and explanation in LearnFree account

  24. Question 24 · Medium

    Iodine is heated with concentrated nitric acid. Which iodine compound is formed?

    1. AHI
    2. BI₂O₅ and NH₃
    3. CHIO₃
    4. DHOI

    Answer and explanation in LearnFree account

  25. Question 25 · Hard

    Taking the lone pairs on the central xenon atom of XeF₂, XeF₄ and XeF₆ together, what is their total number?

    1. A5
    2. B9
    3. C3
    4. D6

    Answer and explanation in LearnFree account

6 more p-Block Elements (Groups 15-18) questions

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