Give the uses of alkali metal elements (group-$I$).

(N/A) Lithium metal is used to make useful alloys,for example with lead to make 'white metal' bearings for motor engines,aluminium to make aircraft parts,and with magnesium to make armour plates. It is used in thermonuclear reactions.
Lithium is also used to make electrochemical cells.
Sodium is used to make a $Na/Pb$ alloy needed to make $PbEt_4$ and $PbMe_4$. These organolead compounds were earlier used as anti-knock additives to petrol,but nowadays vehicles use lead-free petrol.
Liquid sodium metal is used as a coolant in fast breeder nuclear reactors.
Potassium has a vital role in biological systems. Potassium chloride is used as a fertilizer.
Potassium hydroxide is used in the manufacture of soft soap. It is also used as an excellent absorbent of carbon dioxide.