To identify the incorrect statement, let's analyze each option:$\\$Option 1: $$Alkali metals react with water to form their hydroxides.$\\$This statement is correct. Alkali metals like $$Li, Na, K, etc., react with water to form their respective hydroxides and hydrogen gas.$\\$Option 2: $$The oxidation number of K in KO$_2$ is $+4. \\$This statement is incorrect. In potassium superoxide (KO$_2$), the oxidation state of potassium (K) is $+1. \\$The superoxide ion (O$_2^{-}$) has a charge of $-1. \\$Therefore, the oxidation state of K is $+1$ to balance the charge of the superoxide ion.$\\$Option 3: $$Ionisation enthalpy of alkali metals decreases from top to bottom in the group.$\\$This statement is correct. As we move down the group in the periodic table, the atomic size increases, making it easier to remove the outermost electron, thus decreasing the ionization enthalpy.$\\$Option 4: $$Lithium is the strongest reducing agent among the alkali metals.$\\$This statement is correct. Despite having the highest ionization energy among alkali metals, lithium is the strongest reducing agent due to its high hydration energy.$\\$Therefore, the incorrect statement is Option 2.