Question

What is the number of allotropes of selenium?

• A. 2
• B. 4
• C. 5
• D. 6

Hint:

Just like phosphorus has its famous red/white divisions, remember selenium by its two primary forms: red (non-metallic ring structures) and grey (the stable metallic chain conductor form)!

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the total count of primary, well-defined structural allotropic categories recognized for the Group 16 non-metal element Selenium (Se).

Step 2: Detailed Explanation:
Selenium belongs to the oxygen family (chalcogens) and displays prominent allotropic variations matching its periodic neighbors. In foundational chemistry textbooks, selenium is classified as existing primarily in two distinct major macroscopic allotropic forms based on its physical phase arrangement:

• Red Selenium: A non-metallic, crystalline allotrope consisting of puckered $\text{Se}_8$ ring structures, which is soluble in carbon disulfide.

• Grey (Metallic) Selenium: A stable crystalline form consisting of long, helical polymeric chains of selenium atoms. It possesses semi-conducting properties and is the thermodynamically stable form at room temperature.
Therefore, it is officially classified under these two key primary foundational structural frameworks.

Step 3: Final Answer: The primary number of allotropic classifications for selenium is 2, matching option (A).