The standard reduction potential data at 25°C is given below:
$\begin{array}{l} E^{0} ({Fe}^{3 +}, {Fe}^{2 +}) = + 0.77 V; E^{0} ({Fe}^{2 +}, Fe) = - 0.44 V; E^{0} ({Cu}^{2 +}, Cu) = + 0.34 V; E^{0} ({Cu}^{+}, Cu) = + 0.50 V \\ E^{0} (O_{2} (g) + 4 H^{+} + 4 e^{-} \to 2 H_{2} O) = + 1.23 V; E^{0} (O_{2} (g) + 2 H_{2} O + 4 e^{-} \to 4 {OH}^{-}) = + 0.40 V \\ E^{0} ({Cr}^{3 +}, Cr) = - 0.74 V; E^{0} ({Cr}^{2 +}, Cr) = - 0.91 V; \end{array}$
Match E⁰ of the redox pair in Column-I with the values given in List-II and select the correct answer using the code given below the lists.

S.No. Column-I S.No. Column-II
A) $E^{0} ({Fe}^{3 +}, Fe)$ p) –0.18V
B) $E^{0} (4 H_{2} O ⇌ 4 H^{+} + 4 {OH}^{-})$ q) –0.4V
C) $E^{0} ({Cu}^{2 +} + Cu \to 2 {Cu}^{+})$ r) –0.04V
D) $E^{0} ({Cr}^{3 +}, {Cr}^{2 +})$ s) –0.83V

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A - p; B - q;C- r; D - s;

A - r; B -s ;C- q; D - p;

A-r; B-s; C-p; D-q

A - s; B - r;C- p; D - q;

answer is A.

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Detailed Solution

(A) $\to$ r

$\begin{array}{l} 3 e + {Fe}^{3 +} \to Fe, (- 3 \times E_{1}^{0}) \\ e + {Fe}^{3 +} \to {Fe}^{2 +}, (- 1 \times 0.77) \\ 2 e + {Fe}^{2 +} \to Fe, (- 2 \times 0.44) \\ ∴ E_{1}^{0} = - 0.04 \end{array}$

(B) $\to$ s

$\begin{array}{l} O_{2} (g) + 4 H^{+} + 4 e^{-} \to 2 H_{2} O; ∆ G_{1} = - 4 F (1.23) \\ O_{2} (g) + 2 H_{2} O + 4 e^{-} \to 4 {OH}^{-}; ∆ G_{2} = - 4 F (0.40) \\ 4 H_{2} O ⇌ 4 H^{+} + 4 O H^{-}; ∆ G_{3} = - 4 F (E_{3}) \\ ∆ G_{3} = ∆ G_{1} - ∆ G_{2} \\ = 0.4 - 1.23 = - 0.83 V \end{array}$

(C) $\to$ p

$\begin{array}{l} {Cu}^{2 +} + 2 e^{-} \to C u; ∆ G_{1} = - 2 F (0.34); \\ {Cu}^{+} + e^{-} \to Cu; ∆ G_{2} = - F (+ 0.50) \\ C u^{+ 2} + C u \to 2 C u^{+}; ∆ G_{3} = - F E \\ ∆ G_{3} = ∆ G_{1} - ∆ G_{2} = - 0.68 + 0.5 = - 0.18 V \end{array}$

(D) $\to$ q
$\begin{array}{l} {Cr}^{3 +} + 3 e \to Cr; ∆ G_{1} = - 3 F (- 0.74)) \\ {Cr}^{2 +} + 2 e \to Cr; ∆ G_{2} = - 2 F (- 0.91) \\ C r^{+ 3} + e \to C r^{+ 2}; ∆ G_{3} = - F E_{3} \\ ∆ G_{3} = ∆ G_{1} - ∆ G_{2} \\ \Rightarrow E_{3} = - 0.4 V; \end{array}$

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S.No.	Column-I	S.No.	Column-II
A)	$E^{0} ({Fe}^{3 +}, Fe)$	p)	–0.18V
B)	$E^{0} (4 H_{2} O ⇌ 4 H^{+} + 4 {OH}^{-})$	q)	–0.4V
C)	$E^{0} ({Cu}^{2 +} + Cu \to 2 {Cu}^{+})$	r)	–0.04V
D)	$E^{0} ({Cr}^{3 +}, {Cr}^{2 +})$	s)	–0.83V