What is the valency of magnesium with atomic number 12 and sulphur with atomic number 16?

Explanation

(i) Atomic number of magnesium = 12
Electronic configuration is 2, 8, 2.
A magnesium atom can lose its 2 valence electrons to achieve the inert gas electronic configuration of neon (2,8).
Therefore, valency of magnesium = 2.
(ii) The atomic number of sulphur = 16.
Electronic configuration = 2, 8, 6.
A sulphur atom cannot lose 6 electrons to achieve inert gas electronic configuration due to energy consideration. It can gain 2 electrons to achieve the nearest inert gas electronic configuration of argon (2, 8, 8). Thus, the valency of sulphur = 2.