Mercury is transported in metal containers made of

Assertion : Potassium and caesium are used in photoelectric cells.
Reason : Potassium and caesium emit electrons on exposure to light.

Sodium is heated in air at $300^{\circ} C$ to form $X$. $X$ absorbs $CO_2$ and forms $Na_2CO_3$ and $Y$. Which of the following is $Y$?

$A$ $s$-block element $(M)$ reacts with oxygen to form an oxide of the formula $MO_{2}$. The oxide is pale yellow in colour and paramagnetic. The element $(M)$ is:

Which of the following metal oxides decomposes upon heating?

Which of the following is an alkali metal?