CBSE Class 9 Answered

(a) Atom exists in two ways:

1. In the form of molecules -

Molecules can be formed either by the combination of atoms of the same element or of different elements. For ex: O₂ is formed by combination of two Oxygen atoms.
2. In the form of ions -

Ions are formed by the loss or gain of electrons by an atom. for ex: common salt or sodium chloride compound is formed by the collection of millions of sodium ions (Na⁺) and chloride ions (Cl^-).

(b) We cannot see the individual iodine molecules with our eyes because they are very, very small but we can see iodine crystal because it is a collection of millions of iodine molecules held together.