An element X belongs to group 2 and another element Y belongs to group 15 of the periodic table: (a) What is the number of valence electrons in X? (b) What is the valency of X? (c) What the number of valence electrons in Y? (d) What is the valency of Y? Explain how you have arrived at your answers.

For groups 1 and 2, the number of valence electrons is equal to the group number.

Valency is determined by the number of valence electrons present in the atom of the element.

For groups 13 to 18, the number of valence electrons is equal to (group no. - 10).

The number of electrons lost or gained by one atom of an element to achieve the nearest inert gas configuration, gives us the valency.