The incorrect statement is:
(a) Lithium is least reactive with water among the alkali metals
(b) LiCl crystallizes from aqueous solution as $LiCl.2{{H}_{2}}O$
(c) Lithium is the strongest reducing agent among the alkali metals
(d) $Li N{{O}_{3}}$ decomposes on heating to give $Li N{{O}_{2}}$ and ${{O}_{2}}$.

Hint:. Lithium is an alkali metal having higher value of oxidation potential and can easily lose electrons and do not react vigorously with water like the other alkali metals. LiCl is soluble in water and crystallizes in its aqueous form and $Li N{{O}_{3}}$ on decomposition gives lithium oxide. Now identify the incorrect statement.

Complete step by step answer:
Lithium is alkali metal having atomic mass as 3 and mass number as 6 and lies in the first group and second period of the period table and belongs to the s-block elements. Lithium has a strong tendency to lose electrons and acquire the nearest noble gas electronic configuration and thus, act as a strong reducing agent and has a very high value of the oxidation potential as 3.04 V.
All the alkali metals readily react with water to form hydroxides with the release of the hydrogen gas but lithium reacts slowly with water because it has higher activation energy and slower rate of reaction and forms colorless solution of lithium hydroxide along with the release of hydrogen gas.
Lithium chloride consists of lithium and chloride atoms and is white solid which is soluble in water and it crystallizes as $LiCl.2{{H}_{2}}O$.
Lithium nitrate is salt of the lithium and nitric acid and is a white or yellow colored crystalline solid. When lithium nitrate undergoes a decomposition reaction, it results in lithium oxide along with the release of nitrogen dioxide and oxygen gas. The reaction occurs as:
\[4LiN{{O}_{3}}\to{\Delta }2L{{i}_{2}}O+4N{{O}_{2}}+{{O}_{2}}\]

So, from the above given all statements, all are correct except the statement (d).
So, the correct answer is “Option D”.

Note: Lithium reacts with oxygen to form lithium monoxide and lithium peroxide and it has very high specific heat and thermal conductivity but has very low value of density and viscosity too and it reacts with many organic and inorganic reactants too.