Question

Oxygen is divalent, but sulphur exhibits variable valency of 2, 4 and 6 because:
A. Sulphur is less electronegative than oxygen
B. Sulphur is bigger atom than oxygen
C. Ionisation potential of sulphur is more than oxygen
D. Of the presence of d-orbitals in sulphur

Answer 1

The valency can be defined as the combining capacity of an atom. The valency of the element can be expressed as the number of bonds that an atom can form as part of a compound. Depending on this, elements are classified as monovalent, divalent, trivalent etc.

Complete step by step answer:
Monovalent substances are atom, ion, or chemical group which has a valency of one, and can form one covalent bond. Examples are hydrogen, lithium, sodium, chlorine etc
Divalent substances are atom, ion, or chemical group which has a valency of two. Examples are beryllium, oxygen, magnesium, sulphur etc.
Trivalent are atom, ion, or chemical group with a valency of three. Examples are boron, nitrogen, aluminium, phosphorus.
Oxygen is divalent, but sulphur exhibits variable valency of 2, 4 and 6 since the atomic radius of sulphur is larger than that of oxygen, because of the presence of d-orbitals.
The electronic configuration of both oxygen and sulphur are,
${\text{O:1}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{4}}} \\\ {\text{S:}}\left[ {{\text{Ne}}} \right]{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{4}}}{\text{3}}{{\text{d}}^{\text{0}}}$
In sulphur, due to the presence of d orbitals, the excitation of np-electrons to nd-sub-shell gives rise to an increase in the number of unpaired electrons.

Hence, the answer is option B.

Note: Oxygen is also existing as a triatomic molecule in traces, which is called ozone.
Oxygen and sulphur belong to group sixteen of the periodic table. Many elements can be extracted from the sulphide or oxide ores so the members of this group are commonly called chalcogens or ore-forming elements. Combustion is the evolution of heat energy when oxygen combines with elements.