The standard reduction potential data at 25°C is given below. E° (Fe3+, Fe2+) = +0.77 V ; E° (Fe2+, Fe) = –0.44 V E° (Cu2+, Cu) = +0.34 V; E° (Cu+, Cu) = + 0.52 V E° [O2(g) + 4H+ + 4e– → 2H2O] = +1.23 V; E° [O2(g) + 2H2O + 4e– → 4OH¯] = +0.40 V E° (Cr3+, Cr) = – 0.74 V; E°(Cr2+, Cr) = –0.91 V Match E° of the redox pair in List I with the values given in List II and select the correct answer using the code given below the lists: List I List II (P) E° (Fe3+, Fe) (1) – 0.18 V (Q) E° (4H2O ⇌ 4H+ + 4OH¯) (2) – 0.4 V (R) E° (Cu2+ + Cu → 2Cu+) (3) – 0.04 V (S) E° (Cr3+, Cr2+) (4)

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Question

The standard reduction potential data at 25°C is given below.

E° (Fe³⁺, Fe²⁺) = +0.77 V ;

E° (Fe²⁺, Fe) = –0.44 V

E° (Cu²⁺, Cu) = +0.34 V;

E° (Cu⁺, Cu) = + 0.52 V

E° [O₂(g) + 4H⁺ + 4e^– → 2H₂O] = +1.23 V;

E° [O₂(g) + 2H₂O + 4e^– → 4OH¯] = +0.40 V

E° (Cr³⁺, Cr) = – 0.74 V;

E°(Cr²⁺, Cr) = –0.91 V

Match E° of the redox pair in List I with the values given in List II and select the correct answer using the code given below the lists:

P → 2

Q → 3

R → 4

S → 1

P → 4

Q → 1

R → 1

S → 3

P → 1

Q → 2

R → 3

S → 4

P → 3

Q → 4

R → 1

S → 2

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Checking easiest option P or S

$E º = \frac{0 .77 - 2 \times 0 .44}{3} = - 0 .04 V$

Cr³⁺ → Cr²⁺

E° = – 0.74 × 3 + 0.91 × 2

= – 0.4 V

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