Question

In an experiment, $m$ grams of a compound $X$ (gas/liquid/solid) taken in a container is loaded in a balance as shown in figure I below. In the presence of a magnetic filed, the pan with $X$ is either deflected upwards (figure II), or deflected downwards (figure III), depending on the compound $X$. Identify the correct statements(s).

• A. If $X$ is $H _{2} O (l)$, deflection of the pan is upwards.
• B. If $X$ is $K _{4}\left[ Fe ( CN )_{6}\right]$ (s), deflection of the pan is upwards.
• C. If $X$ is $O _{2}(g)$, deflection of the pan is downwards.
• D. If $X$ is $C _{6} H _{6}(I)$, deflection of the pan is downwards.

Answer 1

Answer: (A), (B), (C)

Diamagnetic (all electrons paired) are repelled i.e. magnetized in opposite direction in magnetic field, so such substance are deflected upwards in magnetic field. Diamagnetic substances are
$H _{2} O (\ell), K _{4}\left[ Fe ( CN )_{6}\right], C _{6} H _{6}(\ell)$
Paramagnetic substances (at least one unpaired electron) are attracted in magnetic field, so such substances are deflected downwards.
$O _{2}( g ): \sigma_{1 s ^{2}} \sigma_{1 s ^{2}}^{*} \sigma_{2 s ^{2}} \sigma_{2 p _{x}^{2}} \pi_{2 p _{x}^{2}}=\pi_{2 p _{y}^{2}} \pi_{2 p _{x}^{1}}^{*}=\pi_{2 p _{y}^{1}}^{*}$
Since $O _{2}$ molecules has two unpaired electrons in antibonding $\pi$. MO.
So, $O _{2}$ is paramagnetic.