JEE Main · 2005 · 08 May 2005 · Offline · Chemical Bonding and Molecular Structure

Which one of the following species is diamagnetic in nature?

Answer: (B)

Solution

Magnetic behaviour comes down to whether any electrons are left unpaired, and the molecular-orbital filling settles it. In

H X_{2}

the two electrons both sit paired in the

σ_{1 s}

bonding orbital,

σ_{1 s}^{2}

, leaving nothing unpaired, so the molecule is diamagnetic. Each of the others carries an odd electron:

He X_{2} X^{+}

and

H X_{2} X^{-}

have the arrangement

σ_{1 s}^{2} σ_{1 s}^{* 1}

with a lone electron in the antibonding level, and

H X_{2} X^{+}

has only

σ_{1 s}^{1}

, so all three are paramagnetic. Only

H X_{2}

has every electron paired.

JEE Main · 2005 · 08 May 2005 · Offline · Single correct option