JEE Chemistry 2024 Question with Solution

Given: A list of molecules is to be checked for polarity.

Find: The number of non-polar molecules.

A molecule is non-polar when its net dipole moment is zero, usually because bond dipoles cancel due to symmetry.

From the solution:

• HF: Polar due to significant electronegativity difference.
• $H_2O$: Polar because of bent shape.
• $SO_2$: Polar because of bent shape.
• $H_2$: Non-polar because it is made of identical atoms.
• $CO_2$: Non-polar because linear geometry cancels bond dipoles.
• $CH_4$: Non-polar because tetrahedral symmetry cancels dipoles.
• $NH_3$: Polar because trigonal pyramidal shape gives net dipole.
• HCl: Polar due to electronegativity difference.
• $CHCl_3$: Polar because the molecule is asymmetric.
• $BF_3$: Non-polar because trigonal planar symmetry cancels dipoles.

Thus, the non-polar molecules are $H_2$, $CO_2$, $CH_4$, and $BF_3$.

So, the total number of non-polar molecules is

Therefore, the required answer is $4$.

Given: The molecules must be classified as polar or non-polar.

Find: How many have zero net dipole moment.

Why this works: A quick way is to identify molecules with high symmetry or identical bonded atoms, because such structures often have complete dipole cancellation.

Using this idea:

• $H_2$ is non-polar.
• $CO_2$ is linear and symmetric, so non-polar.
• $CH_4$ is tetrahedral and symmetric, so non-polar.
• $BF_3$ is trigonal planar and symmetric, so non-polar.

The remaining listed molecules have either bent, pyramidal, or asymmetric structures, so they are polar.

Hence, the number of non-polar molecules is $4$.