"Polar covalent bond" is formed through the unequal sharing of electrons between atoms.
Option (a);
EXPLANATION:
Atoms share electrons between each other and create chemical bonds. These are called covalent bonds. These two atoms should have similar affinities to attract electrons, then forms a covalent bond. For example, two hydrogen atoms bond covalently to form an H2 molecule. Now, these bonding electrons can be equal or unequal in number.
When the electrons that are bonded are not equal in number, it forms a polar covalent bond. For example, the formation of an HCL molecule happens by hydrogen molecule and chloride molecule. Electrons attract more with a chlorine atom, so it has a part of negative charge and hydrogen has a partial positive charge in an HCL molecule.