In which of the following cannot sodium metal be stored?

Which of the following absorbs carbon dioxide and releases oxygen?

Which of the following compounds has a positive enthalpy of solution?

Which of the following alkali metals reacts directly with nitrogen?

$A$ metal $(A)$ on heating in nitrogen gas gives compound $(B)$. $(B)$ on treatment with $H_{2}O$ gives a colourless gas which when passed through $CuSO_{4}$ solution gives a dark blue-violet coloured solution. $(A)$ and $(B)$ respectively,are

What are the common physical and chemical features of alkali metals?