The hydration energy of $Mg^{2+}$ is larger than that of

Consider the following statements.
$I$. $Cs^{+}$ ion is more highly hydrated than other alkali metal ions.
$II$. Among the alkali metals,only lithium forms a stable nitride by direct combination with nitrogen.
$III$. Among the alkali metals $Li, Na, K, Rb$,the metal $Rb$ has the highest melting point.
$IV$. Among the alkali metals $Li, Na, K, Rb$,only $Li$ forms peroxide when heated with oxygen.
Select the correct statement.

Match List-$I$ with List-$II$:

List-$I$ (Salt)	List-$II$ (Flame colour wavelength)
$(a)$ $LiCl$	$(i)$ $455.5 \text{ nm}$
$(b)$ $NaCl$	$(ii)$ $670.8 \text{ nm}$
$(c)$ $RbCl$	$(iii)$ $780.0 \text{ nm}$
$(d)$ $CsCl$	$(iv)$ $589.2 \text{ nm}$

Choose the correct answer from the options given below:

Alkali metals react with water to form bases and release hydrogen gas because:

$A$ metal $X$ on heating in a stream of nitrogen gives $Y$. $Y$ on reaction with ${H_2}O$ gives a colorless gas which,when passed through a $CuSO_4$ solution,gives a blue color. What is $Y$?

The commercial method of preparation of potassium by reduction of molten $KCl$ with metallic sodium at $850 ^\circ C$ is based on the fact that: