Question

Elements having valency 'one' are:

(a) always metals

(b) always non-metals

(c) always metalloids

(d) either metals or non-metals

Answer 1

Elements having valency 1 are either metals or non-metals.

Reason:
Elements having valency 1 are placed in the first group of the periodic table known as Alkali metals.
Examples: Sodium, potassium etc.

Hydrogen has some exceptions as Alkali metals.
Hydrogen has valency 1 resembles halogens like fluorine, chlorine which can exist as a diatomic molecule. Hence it can be a nonmetal.