The P-Block Elements NDA Questions

NDA Chemistry

The P-Block Elements MCQ Questions


7.
The STRUCTURE OF AMMONIA (NH₃) has:
A.
Planar triangular geometry with bond angle 120°
B.
T-shaped geometry with bond angle 90°
C.
Linear geometry with bond angle 180°
D.
Trigonal pyramidal geometry with bond angle 107° (less than tetrahedral 109.5° due to lone pair-bond pair repulsion); N-H bond length = 101.7 pm
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ANSWER :
D. Trigonal pyramidal geometry with bond angle 107° (less than tetrahedral 109.5° due to lone pair-bond pair repulsion); N-H bond length = 101.7 pm
8.
The OXIDES OF NITROGEN include multiple compounds. Match the oxidation state of N in each: N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅:
A.
N₂O: −1; NO: −2; N₂O₃: −3; NO₂: −4; N₂O₄: −4; N₂O₅: −5
B.
N₂O: +1; NO: +3; N₂O₃: +2; NO₂: +5; N₂O₄: +4; N₂O₅: +4
C.
N₂O: +1; NO: +2; N₂O₃: +3; NO₂: +4; N₂O₄: +4; N₂O₅: +5
D.
N₂O: +2; NO: +1; N₂O₃: +3; NO₂: +3; N₂O₄: +5; N₂O₅: +4
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ANSWER :
C. N₂O: +1; NO: +2; N₂O₃: +3; NO₂: +4; N₂O₄: +4; N₂O₅: +5
9.
NITRIC ACID (HNO₃) is manufactured by the OSTWALD PROCESS. The steps are:
A.
(i) N₂ + O₂ → 2NO at high T; (ii) 2NO + H₂O → HNO₃ + HNO₂
B.
(i) 4NH₃ + 5O₂ → 4NO + 6H₂O (Pt/Rh catalyst, ~1000 K); (ii) 2NO + O₂ → 2NO₂; (iii) 4NO₂ + O₂ + 2H₂O → 4HNO₃
C.
(i) SO₂ + H₂O → H₂SO₃; (ii) H₂SO₃ + HNO₃ → HNO₃
D.
(i) NH₃ + H₂O → NH₄OH; (ii) NH₄OH + O₂ → HNO₃
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ANSWER :
B. (i) 4NH₃ + 5O₂ → 4NO + 6H₂O (Pt/Rh catalyst, ~1000 K); (ii) 2NO + O₂ → 2NO₂; (iii) 4NO₂ + O₂ + 2H₂O → 4HNO₃
10.
The structure of PHOSPHORUS exists in several ALLOTROPIC FORMS. White phosphorus (P₄) has:
A.
A chain polymeric structure with P-P single bonds throughout
B.
Tetrahedral structure with 4 phosphorus atoms at the corners; P-P-P bond angle = 60° (highly strained); it is very reactive, soft, waxy solid
C.
A layered hexagonal sheet structure like graphite
D.
A simple cubic crystal structure with single P atoms
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ANSWER :
B. Tetrahedral structure with 4 phosphorus atoms at the corners; P-P-P bond angle = 60° (highly strained); it is very reactive, soft, waxy solid
11.
RED PHOSPHORUS differs from WHITE PHOSPHORUS in that red phosphorus:
A.
Has the same P₄ tetrahedral structure but different colour due to impurities
B.
Has the same properties as white phosphorus but lower melting point
C.
Is a polymeric network solid (not P₄ discrete molecules), has higher melting point (~860 K), is non-toxic, non-phosphorescent, insoluble in CS₂, less reactive, and used in safety matchsticks
D.
Is a liquid at room temperature
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ANSWER :
C. Is a polymeric network solid (not P₄ discrete molecules), has higher melting point (~860 K), is non-toxic, non-phosphorescent, insoluble in CS₂, less reactive, and used in safety matchsticks
12.
PHOSPHINE (PH₃) is a hydride of phosphorus. It is prepared by:
A.
Reaction of phosphorus with HCl gas
B.
Hydrolysis of calcium phosphide: Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃↑, or by heating white phosphorus with NaOH: P₄ + 4NaOH + 2H₂O → 2PH₃ + 2NaH₂PO₂
C.
Reduction of PCl₃ with LiAlH₄ only
D.
Heating P₂O₅ with water
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ANSWER :
B. Hydrolysis of calcium phosphide: Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃↑, or by heating white phosphorus with NaOH: P₄ + 4NaOH + 2H₂O → 2PH₃ + 2NaH₂PO₂