(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, 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, potassium are the metals that are unstable because of the unfilled outermost shells. This is the reason that they react with water in order to release hydrogen and these metals are called as alkali metals.

(b) Heliumis the metal that is highly stable and has a filled outermost shells. Helium reacts in severe circumstances and so are called noble or inert gas.