The atomicity of sulphur in orthorhombic sulphur is :
A.$8$
B.$6$
C.$4$
D.$2$

Hint:
Atomicity is defined as the total number of atoms that constitute a molecule. For example, each molecule of oxygen is composed of two oxygen atoms. So atomicity of oxygen is 2.In older contexts, the term atomicity is sometimes used in the same sense as valency.

Complete step by step answer:
Sulphur is a non-metal with atomic number $16$ and atomic mass $32$ . It lies in the column $3$ and the group $16$ of the atomic table. It is abundant, tasteless and odorless. It is yellow crystalline in colour.
Now, we have a brief idea of what Sulphur is and what it looks like. It is important to know that the Sulphur exists in two states in the elemental form. In this one is :
Rhombic, and the other one is
Monoclinic
Orthorhombic sulphur is the sulphur made of the molecules with $8$ sulphur atoms attached to each other. It is predominantly called ${S_8}$ in its molecular integrity.
Now regarding the concept of atomicity, The term atomicity defines the number of persistent atoms in the molecule. Like for the case of Hydrogen, $2{\text{ H}}$ atoms are bonded to form the hydrogen in its elemental state. Therefore its atomicity is $2$, or we can also say that it is diatomic in nature.
Therefore as we can already say that for the case of the sulphur the number of the atoms attached to form up the molecule are $8$, ${S_8}$ in the elemental form.
Therefore, the answer would be option A, $8$ .

Note:
Atomicity differs from element to element as elements may or may not share the same atomicity. But it even differs within the elements, as they exist in multiple physical forms of the elemental state making a new answer for every type of existence.