(a) Lithium, sodium and potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements ? (b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common ?

(a) Lithium, sodium and potassium are all metals that react with water

1.	(a) Lithium, sodium and potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements ? (b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common ?
Answer» Solution :(a) Lithium, sodium and POTASSIUM have the same number of electrons (i.e., 1) in the outermost shell. (b) HELIUM and ARGON have completed outermost shells, 2 electrons in case of helium (completed DUPLET) and 8 electrons in case of argon (completed octet).