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.

answer: -

reaction:

na + cl ⇌ nacl

balanced chemical equation:

na + 2cl ⇌ nacl2

sodium + clorine goes to form sodium chloride (table salt).

the product is nacl2.

and the reactants are na and cl.

(note: if you don’t know what ⇌ means, read below: -

⇌(double head arrow) means reversible reaction).