Which among the following gases is difficult to liquify?

Phenol on heating with zinc dust forms

The degree of dissociation of 0.01 M solution of $\mathrm{NH}_4 \mathrm{OH}$ is $4.2 \times 10^{-2}$. What is the percent dissociation of $\mathrm{NH}_4 \mathrm{OH}$ ?

Which among the following is an example of odd electron molecule?