The elements of group 1 are called alkali metals because:

The correct option is C

Their oxides and hydroxides form alkalies solutions on treating with water.

Explanation for correct option:

(C)

Group1

• Group 1 of the Periodic Table consists of the elements: lithium, sodium, potassium, rubidium, cesium, and francium.
• They are collectively known as alkali metals.

Reason

• Elements present in Group1 are called alkali metals because their oxides and hydroxides form alkalies solutions on treating with water.
• The reaction is as follows:-
• Sodium is an alkali metal, and its oxide is sodium oxide$\left({\mathrm{Na}}_2\mathrm{O}\right)$.
• ${\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{NaOH}\left(\mathrm{aq}\right)$

Explanation for incorrect options:

(A) Oxides of alkali metals form alkaline solutions, not acidic solutions when treated with water.

(B) All alkali metals, with the exception of lithium form peroxides.

(D) The hydroxides of alkali metals form an alkaline solution not an acidic one when treated with water.

Hence, option (C) is correct. The elements of group 1 are called alkali metals because their oxides and hydroxides form alkalies solutions on treating with water.