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 $Y$?

Name the industrially important compounds of $Sodium$.

The atomic radii of alkali metals $(M)$ lie in the order $Li < Na < K < Rb$,but the radii of $M^{+}$ ions in aqueous solution lie in the reverse order $Li^{+} > Na^{+} > K^{+} > Rb^{+}$. What is the reason for this reverse order (on going from $Li$ to $Rb$)?

In which of the following reactions,$MgO$ is not formed?

Two alkali halide salts,$ACl$ and $BCl$,gave crimson red and violet colors in their flame tests,respectively. $A$ and $B$ are respectively:

Which of the following is the most important factor in making lithium metal the strongest reducing agent?