Which of the alkali metals has the least melting point?

Which element in group $IA$ (Alkali metals) exhibits the highest chemical reactivity?

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

List-$I$	List-$II$
$(a)$ $Li$	$(i)$ photoelectric cell
$(b)$ $Na$	$(ii)$ absorbent of $CO_{2}$
$(c)$ $K$	$(iii)$ coolant in fast breeder nuclear reactor
$(d)$ $Cs$	$(iv)$ treatment of cancer
	$(v)$ bearings for motor engines

Choose the correct answer from the options given below:

Which of the following sets represents the alkali metals?

An element $A$ of group $1$ shows similarity to an element $B$ belonging to group $2$. If $A$ has maximum hydration enthalpy in group $1$,then $B$ is:

From the following,which group of elements easily forms a cation?