`P_4` undergoes disproportionation in basic medium to give `PH_3` (phosphine) and `H_2PO^(ɵ)` (dihydrogen hypophoshite ion). Atomic weight of P is 31.

Explanation

To solve the problem of phosphorus undergoing disproportionation in a basic medium to form phosphine (PH₃) and dihydrogen hypophosphite ion (H₂PO₂⁻), we will follow these steps:

### Step 1: Identify the Disproportionation Reaction
Phosphorus (P₄) is undergoing disproportionation, which means it is both oxidized and reduced. The products are phosphine (PH₃) and dihydrogen hypophosphite ion (H₂PO₂⁻).

### Step 2: Write the Half-Reactions
1. **Reduction Half-Reaction**:
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