In the Modern Periodic Table – atoms of all elements are arranged according to the their increasing order of – atomic numbers. An atom of nitrogen has seven protons and seven electrons. State what would be its atomic number.

State the main points of contradiction of Dalton’s atomic theory by the Modern Atomic Theory.

Explain the term – 'atomicity'. Give a reason why –

(a) Helium is considered monoatomic, but hydrogen a diatomic molecule.

(b) Ozone is considered triatomic, but phosphorus a tetratomic molecule.

State the atomicity of the following:

(a) Neon

(b) Oxygen

(c) Chlorine

(d) Argon

(e) Sulphur