The high reactivity and low volatility of white phosphorous is due to:

Options

A. tetrahedrally arrranged `P_(4)` units
B. bond angle of `60^(@)` increases steric (stain) factor
C. weak van der Waals forces of attraction
D. both (B) and ( C)

Explanation

To solve the question regarding the high reactivity and low volatility of white phosphorus, we need to analyze the structural and bonding characteristics of white phosphorus (P4). Here’s a step-by-step solution:

### Step 1: Understand the Structure of White Phosphorus
White phosphorus consists of P4 molecules, where four phosphorus atoms are arranged in a tetrahedral geometry. Each phosphorus atom is bonded to three other phosphorus atoms.

**Hint:** Remember that the arrangement of atoms in a molecule can significantly influence its chemical properties.

### Step 2: Analyze the Hybridization
In P4, the phosphorus atoms undergo sp³ hybridization. This means that one s orbital and three p orbitals mix to form four equivalent sp³ hybrid orbitals.

**Hint:** Hybridization helps in determining the shape and bond angles in a molecule.

### Step 3: Identify the Bond Angles
In a perfect tetrahedral arrangement, the bond angles are approximately 109.5 degrees. However, in P4, the bond angles are approximately 60 degrees due to the tetrahedral arrangement of four phosphorus atoms.

**Hint:** Compare the bond angles in ideal tetrahedral geometry with those in P4 to understand the strain involved.

### Step 4: Discuss the Consequences of the Bond Angle
The bond angle of 60 degrees in P4 leads to significant steric strain. This strain makes the molecule unstable, contributing to its high reactivity. The instability arises because the phosphorus atoms are forced closer together than they would prefer, creating a situation where the bonds are under tension.

**Hint:** Steric strain can make a molecule more reactive because it seeks to relieve the strain by undergoing chemical reactions.

### Step 5: Consider the Role of Van der Waals Forces
While weak van der Waals forces are present in P4, they are not the primary reason for the high reactivity and low volatility of white phosphorus. The significant steric strain due to the bond angles plays a more crucial role.

**Hint:** Always evaluate the significance of different factors when determining the properties of a compound.

### Conclusion
The high reactivity and low volatility of white phosphorus can be attributed primarily to the bond angle of 60 degrees that increases steric strain, making it unstable and highly reactive.

### Final Answer
The correct option is **B: The bond angle of 60 degrees increases steric strain.**