Thermodynamically most stable allotrope of phosphorus is :

Options

A. Red
B. White
C. Black
D. Yellow

Explanation

To determine the thermodynamically most stable allotrope of phosphorus, we can follow these steps:

### Step 1: Understand the Allotropes of Phosphorus
Phosphorus exists in several allotropes, the most common being white phosphorus, red phosphorus, and black phosphorus. Each allotrope has distinct properties and stability.

**Hint:** Research the different allotropes of phosphorus and their characteristics.

### Step 2: Analyze the Stability of Each Allotrope
- **White Phosphorus:** This allotrope is highly reactive and less stable due to its P4 tetrahedral structure. It is known to ignite in air and is considered the least stable form.
- **Red Phosphorus:** This allotrope is more stable than white phosphorus but still less stable than black phosphorus. It has a network structure that makes it less reactive.
- **Black Phosphorus:** This is the least reactive and most stable allotrope of phosphorus at room temperature and pressure. It has a layered structure similar to graphite, which contributes to its stability.

**Hint:** Consider the reactivity and structural characteristics of each allotrope when assessing stability.

### Step 3: Identify the Conditions for Stability
Black phosphorus can be synthesized from white phosphorus by applying high pressure (around 12,000 atmospheres). This transformation indicates that black phosphorus is thermodynamically favored under certain conditions.

**Hint:** Think about how pressure and temperature can influence the stability of different allotropes.

### Step 4: Conclude the Most Stable Allotrope
Based on the analysis, black phosphorus is identified as the thermodynamically most stable allotrope of phosphorus at room temperature and pressure.

**Hint:** Summarize the findings and confirm the conclusion based on the properties and stability of each allotrope.

### Final Answer
The thermodynamically most stable allotrope of phosphorus is **black phosphorus**.