The correct option for the question "A molecule of phosphorus is" is **C. tetraatomic**. ### Detailed Explanation 1. **Understanding Phosphorus Molecules**: - Phosphorus is a chemical element with the symbol **P** and atomic number **15**. In its most common form, phosphorus exists as a molecule made up of four phosphorus atoms. This form is known as **white phosphorus** (P₄). - The tetraatomic nature of phosphorus means that each molecule consists of four atoms bonded together. 2. **Structure of P₄**: - The P₄ molecule has a tetrahedral shape, where the four phosphorus atoms are arranged at the corners of a tetrahedron. This arrangement is due to the bonding angles and the repulsion between the electron pairs surrounding each phosphorus atom. - Each phosphorus atom in the P₄ molecule forms three single covalent bonds with its neighboring phosphorus atoms, resulting in a stable structure. 3. **Why Option C is Correct**: - Since a molecule of phosphorus (specifically white phosphorus) consists of four atoms, it is classified as tetraatomic. This is the defining characteristic of the phosphorus molecule in its most common allotrope. ### Why the Other Options are Incorrect - **Option A: Diatomic**: - A diatomic molecule consists of two atoms. Examples include O₂ (oxygen) and N₂ (nitrogen). Phosphorus does not exist as a diatomic molecule in its common forms, making this option incorrect. - **Option B: Triatomic**: - A triatomic molecule consists of three atoms. An example is O₃ (ozone). Phosphorus does not naturally form a stable triatomic molecule, so this option is also incorrect. - **Option D: Monoatomic**: - A monoatomic molecule consists of a single atom. Noble gases like helium (He) and neon (Ne) are examples of monoatomic gases. Phosphorus does not exist as a monoatomic species under normal conditions, making this option incorrect as well. ### Summary of Key Points - Phosphorus commonly exists as a tetraatomic molecule (P₄). - The P₄ molecule has a tetrahedral structure with four phosphorus atoms bonded together. - Diatomic, triatomic, and monoatomic options do not accurately describe the common forms of phosphorus. - Understanding the molecular structure of elements is crucial for grasping their chemical behavior and properties. This thorough understanding of phosphorus and its molecular structure will help you in your chemistry studies and exams.