Polarity is important because
a) polar and nonpolar molecules have properties.
b) polar molecules interact strongly with molecules but do not interact with molecules,
c) nonpolar molecules interact strongly with molecules but do not interact with molecules.

a) different properties

b) interact strongly with polar molecules; don't interact with non-polar molecules

c) interact strongly with nonpolar molecules; don't interact with polar molecules

Explanation:          

In a molecule, when a covalent bond is formed by the unequal sharing of electrons, it leads to separation of charges. Such a molecule is known as a polar molecule and the bond is called the polar bond.

Whereas, there is no separation of charge in a non-polar molecule.

Polar molecules are strongly attracted to polar molecules and interact through dipole–dipole intermolecular forces and hydrogen bonds.

Whereas, non-polar molecules are strongly attracted and interact with non-polar molecules.

Therefore, polar molecules do not interact with non-polar molecules and vice versa, as they have different properties.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.