Correct Answer - B
The reaction of alkali metals with water becomes increasingly violent on descending the group because the melting point of alkali metals decreases form Li to Cs. The melting points of alkali metals from Na to Cs are so low that the heat of reaction is sufficient to melt them or even vaporize. The molten metal spreads out, exposing therby a larger surface area to the water. Thus, metal reacts even faster, gets even hotter, and catches fire. The melting point of Li is relatively high. The heat of reaction is not sufficiently large enough to melt it. Thus, Li metal reacts gently with water.
(1) `2M(s)+2H_(2)O(1)to2M^(+)OH(aq.)+H_(2)(g)`. The resulting aqueous solution is alkaline due to the formation of hydroxides.
(3) Li metal liberates maximum energy because it has the most negative standard reduction electrode potential `(DeltaG^(@)=-nFE^(@))`.
