A black coloured element with $n s^2 n p^1$ outer electronic configuration cannot react with air in its crystalline form. However, in amorphous form, it gives an oxide in air which is acidic in nature. Identify the element.

The element that does not show catenation is

In the following, the oxoacid with a peroxy bond is

Chlorine is allowed to react with excess of ammonia. In this, 1 mole of chlorine can oxidise ' $Z$ ' moles of $\mathrm{NH}_3$. ' $Z$ ' is