Question 1
What is the valency of an element?
The right answer is the one marked above.
The number of hydrogen atoms that can combine with one atom of that element, or be replaced by it. Valency is the combining capacity of an atom, and it is measured relative to hydrogen.
In a chemical combination it equals the number of electrons removed from an atom, or gained by it, or the number of electron pairs shared between atoms. The electrons in the last energy level — the valence electrons — are generally equal to the element's maximum valency.