Level 1 — Recognitionp-Block

p-Block

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Chapter: p-Block (Groups 13–18) Level: 1 — Recognition (MCQ, Matching, True/False with justification) Time Limit: 20 minutes Total Marks: 30

Section A — Multiple Choice Questions (1 mark each) — 10 marks

Q1. In diborane ( $B_2H_6$ ), the number of 3-centre-2-electron (banana) bonds is: (a) 1 (b) 2 (c) 3 (d) 4

Q2. The correct order of Lewis acid strength of boron trihalides is: (a) $BF_3 > BCl_3 > BBr_3$ (b) $BBr_3 > BCl_3 > BF_3$ (c) $BCl_3 > BBr_3 > BF_3$ (d) $BF_3 > BBr_3 > BCl_3$

Q3. Borazine ( $B_3N_6H_6$ commonly $B_3N_3H_6$ ) is called "inorganic benzene" because it: (a) contains only carbon rings (b) is isoelectronic and isostructural with benzene (c) is a strong acid (d) is coloured

Q4. Which allotrope of carbon is a two-dimensional single layer of $sp^2$ carbon atoms? (a) diamond (b) graphite (c) graphene (d) fullerene

Q5. The oxide of nitrogen that is a colourless neutral gas and is also called laughing gas is: (a) $NO$ (b) $NO_2$ (c) $N_2O$ (d) $N_2O_5$

Q6. The basicity of $H_3PO_3$ (phosphorous acid) is: (a) 1 (b) 2 (c) 3 (d) 4

Q7. The correct order of acid strength among oxoacids of chlorine is: (a) $HClO > HClO_2 > HClO_3 > HClO_4$ (b) $HClO_4 > HClO_3 > HClO_2 > HClO$ (c) $HClO_2 > HClO > HClO_4 > HClO_3$ (d) all equal

Q8. Molecular shape of $XeF_4$ is: (a) tetrahedral (b) square planar (c) see-saw (d) octahedral

Q9. The catalyst used in the Contact process for manufacture of $H_2SO_4$ is: (a) Fe (b) Pt gauze (c) $V_2O_5$ (d) $Al_2O_3$

Q10. Ozone ( $O_3$ ) has a molecular shape that is: (a) linear (b) bent (angular) (c) trigonal planar (d) pyramidal

Section B — Matching (2 marks each) — 8 marks

Q11. Match Column I (process) with Column II (product):

Column I	Column II
(i) Haber process	(P) $HNO_3$
(ii) Ostwald process	(Q) $NH_3$
(iii) Contact process	(R) $Al$
(iv) Hall–Héroult	(S) $H_2SO_4$

Q12. Match Column I (Xe compound) with Column II (shape):

Column I	Column II
(i) $XeF_2$	(P) square pyramidal
(ii) $XeF_4$	(Q) pyramidal
(iii) $XeF_6$	(R) linear
(iv) $XeO_3$	(S) square planar

Q13. Match Column I (species) with Column II (bonding feature):

Column I	Column II
(i) Diamond	(P) 3c-2e bond
(ii) Graphite	(Q) $sp^3$ 3-D network
(iii) $B_2H_6$	(R) 3-D silicate framework
(iv) Zeolite	(S) $sp^2$ layered, delocalised electrons

Q14. Match Column I (halogen fact) with Column II:

Column I	Column II
(i) Strongest oxidising halogen	(P) HI
(ii) Strongest hydrohalic acid	(Q) $F_2$
(iii) Example of pseudohalogen	(R) $ICl$
(iv) Example of interhalogen	(S) $(CN)_2$

Section C — True/False WITH Justification (2 marks each: 1 T/F + 1 reason) — 12 marks

Q15. "Boron shows a diagonal relationship with silicon." State True/False and justify.

Q16. " $N_2$ is inert at room temperature because of its weak single bond." State True/False and justify.

Q17. " $H_3PO_4$ is a stronger reducing agent than $H_3PO_3$ ." State True/False and justify.

Q18. "White phosphorus is more reactive and less stable than red phosphorus." State True/False and justify.

Q19. "Ozone in the stratosphere protects life by absorbing UV radiation." State True/False and justify.

Q20. " $BF_3$ is a weaker Lewis acid than $BCl_3$ due to back-bonding from F to B." State True/False and justify.

Answer keyMark scheme & solutions

Section A (1 mark each)

Q1. (b) 2. Diborane has two bridging H atoms, each forming one 3c-2e bond. (1)

Q2. (b) $BBr_3 > BCl_3 > BF_3$ . Lewis acidity increases down the halogens because back-bonding (X→B $p_\pi$ – $p_\pi$ ) is strongest for F (best size match) making $BF_3$ least acidic. (1)

Q3. (b) isoelectronic and isostructural with benzene. Borazine $B_3N_3H_6$ is a planar 6-membered ring. (1)

Q4. (c) graphene — single 2-D $sp^2$ layer. (1)

Q5. (c) $N_2O$ — laughing gas, neutral colourless. (1)

Q6. (b) 2. $H_3PO_3$ has two P–OH groups (one P–H bond is non-ionisable), so it is dibasic. (1)

Q7. (b) $HClO_4 > HClO_3 > HClO_2 > HClO$ . Acidity increases with oxidation state / number of terminal O atoms (better anion stabilisation). (1)

Q8. (b) square planar. $XeF_4$ : $sp^3d^2$ , 2 lone pairs axial. (1)

Q9. (c) $V_2O_5$ . (1)

Q10. (b) bent (angular), ~117°, central O has one lone pair. (1)

Section B (2 marks each — 0.5 per correct pair)

Q11. (i)–Q, (ii)–P, (iii)–S, (iv)–R (2)

Q12. (i)–R, (ii)–S, (iii)–P, (iv)–Q. ( $XeF_6$ distorted octahedral/related to square pyramidal geometry description; $XeO_3$ pyramidal.) (2)

Q13. (i)–Q, (ii)–S, (iii)–P, (iv)–R (2)

Q14. (i)–Q, (ii)–P, (iii)–S, (iv)–R (2)

Section C (2 marks each: 1 for T/F, 1 for justification)

Q15. True (1). B and Si lie diagonally; both are semi-metals/metalloids, form covalent acidic oxides, weak amphoteric/acidic behaviour, and hydrides — similar charge/radius ratio. (1)

Q16. False (1). $N_2$ is inert due to a very strong triple bond ( $N\equiv N$ , bond energy ≈ 941 kJ/mol), not a weak single bond. (1)

Q17. False (1). $H_3PO_3$ (contains a P–H bond, P in +3) is the stronger reducing agent; $H_3PO_4$ (P in +5, no P–H) is not a reducing agent. (1)

Q18. True (1). White P has angular strain in the $P_4$ tetrahedron (60° bond angles), making it more reactive and thermodynamically less stable than red P (polymeric). (1)

Q19. True (1). Stratospheric $O_3$ absorbs harmful UV-B/UV-C radiation (via $O_3 \rightleftharpoons O_2 + O$ ), shielding living organisms. (1)

Q20. True (1). In $BF_3$ , filled F $2p$ orbitals back-donate into the empty B $2p$ orbital (good size overlap), reducing B's electron deficiency; overlap is poorer in $BCl_3$ , so $BCl_3$ is the stronger Lewis acid. (1)

[
  {"claim": "Basicity of H3PO3 is 2 (two ionisable OH)", "code": "ionisable_OH = 2; result = (ionisable_OH == 2)"},
  {"claim": "Diborane has 2 three-centre-two-electron bonds", "code": "bridging_H = 2; bonds_3c2e = bridging_H; result = (bonds_3c2e == 2)"},
  {"claim": "Cl oxoacid acidity increases with oxidation state HClO<HClO2<HClO3<HClO4", "code": "ox = {'HClO':1,'HClO2':3,'HClO3':5,'HClO4':7}; order = sorted(ox, key=lambda k: ox[k]); result = (order == ['HClO','HClO2','HClO3','HClO4'])"},
  {"claim": "N2 triple bond energy ~941 kJ/mol far exceeds a typical single bond ~160", "code": "triple = 941; single = 160; result = (triple > 5*single)"}
]