Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.
Lithium, sodium and potassium are all metals which belong to group 1, and have 1 valence electron in their atoms. They all have the same electronic configuration. Therefore, each element shows similar chemical properties when reacting with water and liberates hydrogen gas.