Assertion (A) The ionic radii of the alkaline earth metals are smaller than those of alkali metals in the same period.

Reason (R) Alkali metals have higher nuclear charge than that of the alkaline earth metals.

The correct option among the following is

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

From the following compounds, the ones which contain both $s p$ and $s p^2$ hybridised carbons are