The metal that forms nitride by reacting directly with $N_2$ of air is

Which of the following metals is found in the green colouring pigment chlorophyll of plants?

$2Na_2O \overset{400 \ ^oC}{\rightleftharpoons} A + 2Na$
$A + SO_2 \to Na_2SO_4$
$A + CO \to Na_2CO_3$
In the above reaction,$A$ is:

Which element from the following forms a chlorophyll complex?

The correct order of increasing ionic character among $LiH$,$NaH$,$KH$,$RbH$,$CsH$ is

An ore of potassium is