Standard reduction potential values for P, Q, R and S are +0.34V, 0.76V, +0.0V and 3.05V, respectively. What is the correct order of their reducing power ? a) P R Q S b) S R Q P c) Q P S R d) S Q R P

The reducing power of a species is inversely proportional to its standard reduction potential ($E^{\circ }$). A more negative $E^{\circ }$ indicates a stronger reducing agent.

Given:

• $E^{\circ }$ of P = +0.34 V
• $E^{\circ }$ of Q = -0.76 V
• $E^{\circ }$ of R = +0.0 V
• $E^{\circ }$ of S = -3.05 V

Ordering by reducing power (most reducing → least reducing):

1. S ($-3.05$ V, strongest reducing agent)
2. Q ($-0.76$ V)
3. R ($+0.0$ V)
4. P ($+0.34$ V, weakest reducing agent)

Thus, the correct order is S > Q > R > P, which corresponds to option (d).