(a) Phosphourous `(P_4)` and vanadium `(V)` both exhibit variable oxidation states but due to different reason.
(b) Name the transition metal which does not show variable O.S.

Explanation

### Step-by-Step Solution

#### Part (a): Variable Oxidation States of Phosphorus and Vanadium

1. **Understanding Phosphorus (P₄)**:
- Phosphorus has an atomic number of 15, and its electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^3\).
- The outer shell has 5 electrons (2 in the s subshell and 3 in the p subshell).
- Phosphorus can exhibit oxidation states of -3, +3, and +5:
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