It is easier to determine the electron configurations for the p-block elements in periods 1, 2, and 3 than to determine the electron configurations for the rest of the p-block elements in the periodic table because
a. they have a larger number of core electrons.
b. their electrons are assigned to s and p orbitals only.
c. their electrons are placed in a higher number of orbitals.
d. they have more valence electrons available for bonding.

b.their electrons are assigned to s and p orbitals only.

Explanation:

Electron configuration of He, B and Al the elements that lie in the first, second and third period of the periodic table respectively as follows:

He:  1s²

B:  [He] 2s² 2p¹

Al:  [Ne] 3s² 3p¹

Ga:  [Ar] 3d¹⁰ 4s²  4p¹

In Ga, element ling in the 4th period, electrons enter the s, p and d orbitals.  So before assigning electrons to the p orbitals it is important to ensure that the d orbital is  either partially or fully filled.

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.