The number of non-polar molecules from the following is ____ \(\mathrm{HF}, \mathrm{H}_{2} \mathrm{O}, \mathrm{SO}_{2}, \mathrm{H}_{2}, \mathrm{CO}_{2}, \mathrm{CH}_{4}, \mathrm{NH}_{3}, \mathrm{HCl}, \mathrm{CHCl}_{3}, \mathrm{BF}_{3}\)

JEE Main · 2024 · 27 Jan 2024 · Shift 2 · Chemical Bonding and Molecular Structure

The number of non-polar molecules from the following is ____

HF, H_{2} O, SO_{2}, H_{2}, CO_{2}, CH_{4}, NH_{3}, HCl, CHCl_{3}, BF_{3}

Answer: 4

A molecule is non-polar when it has no polar bonds, or when its polar bond dipoles cancel by symmetry.

H F

and

H C l

are polar diatomics with an unbalanced bond dipole.

H_{2} O

(bent) and

S O_{2}

(bent, with a lone pair on S) both have a net dipole.

N H_{3}

(pyramidal) has a net dipole along the lone pair.

C H C l_{3}

is tetrahedral but the four substituents are not identical, so its dipoles do not cancel.

H_{2}

has no bond dipole at all.

C O_{2}

is linear, so its two C=O dipoles point in opposite directions and cancel.

C H_{4}

is a perfectly symmetric tetrahedron, so its four C–H dipoles cancel.

B F_{3}

is trigonal planar, so its three B–F dipoles cancel.

The non-polar molecules are

H_{2}, C O_{2}, C H_{4}

and

B F_{3}

— four in total.

JEE Main · 2024 · 27 Jan 2024 · Shift 2 · Integer answer