Question

The valency, which is the combining capacity of oxygen is two:
A.True
B.False

Answer 1

Valency is the combining power of an element. Elements in the same group of the periodic table have the same valency. The valency of an element is related to how many electrons are in the outer shell. The noble gases have the valency zero as they do not usually combine with other elements.

Complete answer:
The valency of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. The combining capacity, or affinity of an atom of a given element is determined by the number of hydrogen atoms that it combines with. In oxygen has a valency of $2$. Valence diagrams of a compound represent the connectivity of the elements, with lines drawn between two elements, sometimes called bonds, representing a saturated valency for each element.
Electronic configuration of oxygen is $[He]2{s^2},2{p^4}$ i.e $2,8,6$
The valency of oxygen is $2$, because it needs two atoms of hydrogen to form water. Electrons only pair up if there are no empty orbitals; you end up with one full orbital with paired electrons that takes extra energy to break up and two orbitals with single electrons that are easily ionized. Two easily ionized electrons means a valence of $2$ for Oxygen.
So, the correct answer is (A) True.

Note:
The difference between the valency and oxidation state is that Valency is the number of electrons present in the outermost shell of a particular element whereas oxidation state is the number of electrons that an element in a particular compound has lost or gained. This is the main difference between valency and oxidation state.