Correct Answer - A
Both m.p. and heat of the reaction of alkali metals with `H_(2)O` decreases down the group from Li to Cs .
Although the heat of reaction of Li is the highest but due to its high melting point , even the heat is not sufficient to melt the metal thereby exposing greater surface to water for reaction . as a result , Li has the least reactivity by the reactivity increases as the m.p. of the alkali metals decrease down the group from Li to Cs .
