Question: 62: Identify the incorrect statement from the following
(1) Ionisation enthalpy of alkali metals decreases from top to bottom in the group.
(2) Lithium is the strongest reducing agent among the alkali metals.
(3) Alkali metals react with water to form their hydroxides.
(4) The oxidation number of K in \mathrm{KO}_{2} is +4 .
Answer: Option (4)
Explanation:
The ionisation enthalpy of alkali metals decreases down the group due to an increase in atomic size
and shielding effect, which makes removal of the outermost electron easier.
Lithium is the strongest reducing agent among alkali metals in aqueous solution because it has the highest hydration enthalpy, which compensates for its higher ionisation enthalpy.
Alkali metals readily react with water to form their corresponding hydroxides and hydrogen gas.
In the compound \mathrm{KO}_{2}, potassium forms a superoxide ion.
The superoxide ion has an overall charge of -1. Since potassium is an alkali metal,
it always shows an oxidation number of +1 in its compounds.
Therefore, the statement that the oxidation number of potassium in
\mathrm{KO}_{2} is +4 is incorrect.