(i) How do you calculate the possible valency of an element from the electronic configuration of its atoms?

(ii) Calculate the valency of an element X whose atomic number is 9.

(i) The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom:

• If the number of valence electrons is $1, 2, 3,$ or $4$, the valency is equal to the number of valence electrons.
• If the number of valence electrons is $5, 6, 7,$ or $8$, the valency is calculated as $8 - \text{number of valence electrons}$.

(ii) For element X with atomic number $9$:

• Electronic configuration: $2, 7$
• Number of valence electrons = $7$
• Valency = $8 - 7 = 1$