JEE Chemistry 2024 Question with Solution

Given: The molecules are $CH_4$, $BF_3$, $H_2O$, $HF$, $NH_3$, $CO_2$, and $SO_2$.

Find: The total number of molecules having zero dipole moment.

A molecule has zero dipole moment when its bond dipoles cancel because of symmetric geometry.

• $CH_4$: tetrahedral and symmetric, so dipole moment is zero.
• $BF_3$: trigonal planar and symmetric, so dipole moment is zero.
• $H_2O$: bent geometry, so dipole moment is non-zero.
• $HF$: heteronuclear diatomic molecule, so dipole moment is non-zero.
• $NH_3$: trigonal pyramidal geometry, so dipole moment is non-zero.
• $CO_2$: linear and symmetric, so dipole moment is zero.
• $SO_2$: bent geometry, so dipole moment is non-zero.

Thus, the molecules with zero dipole moment are $CH_4$, $BF_3$, and $CO_2$.

Therefore, the total number of such molecules is $3$. The correct option is A.

Given: The list of molecules is $CH_4$, $BF_3$, $H_2O$, $HF$, $NH_3$, $CO_2$, and $SO_2$.

Find: How many have zero dipole moment.

Use symmetry directly:

• Symmetric molecules usually have cancellation of bond dipoles.
• Bent or pyramidal molecules usually have a net dipole moment.

So, $CH_4$, $BF_3$, and $CO_2$ are symmetric and have zero dipole moment, while $H_2O$, $HF$, $NH_3$, and $SO_2$ do not.

Therefore, the total number is $3$, so the correct option is A.