Which of the following alkali metals reacts directly with nitrogen?

$A$ certain metal is used in the preparation of an antacid. This metal accidentally catches fire,which cannot be extinguished using $CO_2$. Which metal is this?

Choose the alkali metal with the highest reactivity among the following.

The electronic configuration of a metal is $1s^2 2s^2 2p^6 3s^1$. The formula of its oxide is:

What is caused by an excess of $Na^{+}$ ions in the human body?

Which one of the following compounds in aqueous solution gives a white precipitate with perchloric acid?