(a) By the sharing of electrons between two atoms?

(b) By the transfer of electrons from one atom to another?

Solution:

(a) Covalent bond is the bond formed by sharing of electrons between two atoms

(b) Ionic bond is the bond formed by transferring electrons from one atom to another.

Explanation:

(a) A covalent bond is a chemical link established by the sharing of electrons between two atoms. The electron pairs, also known as molecular bonds, cause a steady equilibrium of attractive and repulsive forces between the atoms.

(b) An ionic bond is a chemical bond generated by the transfer of electrons from one atom to another. The metal loses electrons and produces a positively charged cation, while nonmetals absorb those electrons and form a negatively charged anion.