(a) Lithium, sodium, 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 have following similarties:

(i) These all are belong to same group (Group I ) in the preiodic table.

(ii) They all have 1 electrone in their valene sheel.

(iii) They all are alkali metals.

(iv) They all are highly reactive.

(b) Helium and neaon both are noble gas which belong the zero group in the modern periodic table. The common thing between helium and neon is that both have outermost shell completely filled with electrons. Helium has two electrons in its K shell whereas neon has 8 electrons in its outermost shell.