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NEET CHEMISTRYMedium

The incorrect statement among the following regarding the molecules of CH4\text{CH}_4, NH3\text{NH}_3, and H2O\text{H}_2\text{O} is:

A

The H-O-H bond angle in H2O\text{H}_2\text{O} is larger than the H-C-H bond angle in CH4\text{CH}_4.

B

The H-O-H bond angle in H2O\text{H}_2\text{O} is smaller than the H-N-H bond angle in NH3\text{NH}_3.

C

The H-C-H bond angle in CH4\text{CH}_4 is larger than the H-N-H bond angle in NH3\text{NH}_3.

D

The H-C-H bond angle in CH4\text{CH}_4, the H-N-H bond angle in NH3\text{NH}_3, and the H-O-H bond angle in H2O\text{H}_2\text{O} are all greater than 9090^\circ.

Step-by-Step Solution

According to VSEPR theory, the central atoms in CH4\text{CH}_4, NH3\text{NH}_3, and H2O\text{H}_2\text{O} all undergo sp3sp^3 hybridisation. However, they possess different numbers of lone pairs: carbon in CH4\text{CH}_4 has 0, nitrogen in NH3\text{NH}_3 has 1, and oxygen in H2O\text{H}_2\text{O} has 2 lone pairs. Because lone pair-lone pair repulsion is stronger than lone pair-bond pair repulsion, which is in turn stronger than bond pair-bond pair repulsion, the bond angle decreases as the number of lone pairs increases.

  • In CH4\text{CH}_4, the bond angle is the ideal tetrahedral angle of 109.5109.5^\circ.
  • In NH3\text{NH}_3, the presence of one lone pair compresses the H-N-H angle to 107107^\circ.
  • In H2O\text{H}_2\text{O}, the presence of two lone pairs compresses the H-O-H angle further to 104.5104.5^\circ. As all these angles (109.5109.5^\circ, 107107^\circ, and 104.5104.5^\circ) are greater than 9090^\circ, option 4 is correct. The correct order of bond angles is CH4>NH3>H2O\text{CH}_4 > \text{NH}_3 > \text{H}_2\text{O}. Therefore, the statement claiming that the H-O-H bond angle in H2O\text{H}_2\text{O} is larger than the H-C-H bond angle in CH4\text{CH}_4 is factually incorrect.
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