The question asks about the atomicity of Phosphorous and provides several options to choose from.

Let us analyze Phosphorous:

Atomicity: Atomicity refers to the number of atoms present in a molecule of an element. For instance, if a molecule contains two atoms, it is termed as diatomic.

The element phosphorus commonly exists in nature in different allotropic forms, including:

• White Phosphorus: In this form, phosphorus exists as \(P_4\) molecules. This means each molecule of phosphorus contains 4 atoms, hence it is tetra-atomic.
• Other forms include: Red phosphorus and black phosphorus. However, these forms are generally polymeric in nature and do not have a defined small number of atoms like \(P_4\).

Among the options provided:

1. Tetra-atomic: This corresponds to the common molecular form of white phosphorus, \(P_4\). Therefore, this is the correct option.
2. Monoatomic: This implies a single atom, which does not apply here because phosphorus does not naturally exist as monoatomic.
3. Poly-atomic: This is a broad categorization and could imply any number of atoms greater than one. While technically true, it is not specific.
4. Diatomic: This implies a molecule composed of two atoms, which is not applicable to common phosphorus allotropes.

Conclusion: The atomicity of a phosphorus molecule in its common white phosphorus form is tetra-atomic, as it consists of four phosphorus atoms per molecule.