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.
$O_2(g):{\sigma }_{1s^2}{\sigma }_{1s^2}^{\ast }{\sigma }_{2s^2}{\sigma }_{2p_x^2}{\pi }_{2p_x^2}={\pi }_{2p_y^2}{\pi }_{2p_x^1}^{\ast }={\pi }_{2p_y^1}^{\ast }$
Since $O_2$ molecules has two unpaired electrons in antibonding $\pi$. MO.
So, $O_2$ is paramagnetic.