JEE Main 2025 Jan 24 Shift 1, Chemistry Q18: Valence Bond Theory And Hybridisation

JEE Main2025Jan 24, Shift 1Chemistry

Which of the following statement is true with respect to H $_{2}$ O, NH $_{3}$ and CH $_{4}$ ?

A. The central atoms of all the molecules are sp $^{3}$ hybridized.

B. The H $-$ O $-$ H, H $-$ N $-$ H and H $-$ C $-$ H angles in the above molecules are 104.5 $^{\circ}$ , 107.5 $^{\circ}$ and 109.5 $^{\circ}$ respectively.

C. The increasing order of dipole moment is CH $_{4}$ $<$ NH $_{3}$ $<$ H $_{2}$ O.

D. Both H $_{2}$ O and NH $_{3}$ are Lewis acids and CH $_{4}$ is a Lewis base

E. A solution of NH $_{3}$ in H $_{2}$ O is basic. In this solution NH $_{3}$ and H $_{2}$ O act as Lowry-Bronsted acid and base respectively.

Choose the correct answer from the options given below :

A
A, B and C only
B
C, D and E only
C
A, D and E only
D
A, B, C and E only

Solution

Assess each statement:

A. In each of H $_{2}$ O, NH $_{3}$ and CH $_{4}$ the central atom has four electron domains (bonding pairs $+$ lone pairs summing to 4), so all are sp $^{3}$ hybridised. $✓$

B. The bond angles compress as lone pairs replace bonding pairs (lone pair $-$ bond pair repulsion is larger than bond pair $-$ bond pair): CH $_{4}$ has no lone pairs ( $109. 5^{\circ}$ ), NH $_{3}$ has one ( $107. 5^{\circ}$ approx.), H $_{2}$ O has two ( $104. 5^{\circ}$ ). $✓$

C. Dipole moments increase as electronegativity of the central atom rises and as more lone pairs reinforce the net dipole: $μ (C H_{4}) = 0 < μ (N H_{3}) \approx 1.47 D < μ (H_{2} O) \approx 1.85 D$ . $✓$

D. H $_{2}$ O and NH $_{3}$ have lone pairs they donate, so they are Lewis bases, not acids. CH $_{4}$ has no lone pair and no empty low-lying orbital; it is neither. $\times$

E. In NH $_{3}$ (aq), NH $_{3}$ accepts a proton from water, so NH $_{3}$ acts as the Bronsted base and H $_{2}$ O acts as the Bronsted acid $-$ the roles are reversed from what statement E claims. $\times$

Correct statements: A, B and C. $∴$ Option (1).

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JEE Main 2025 Jan 24 Shift 1, Chemistry Q18: Valence Bond Theory And Hybridisation

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