Question: The standard electrode potential $\left(E^{\circ}\right)$ values of $\mathrm{Al}^{3+} / \mathrm{Al}, \mathrm{Ag}^{+} / \mathrm{Ag}, \mathrm{K}^{+} / \mathrm{K}$ and $\mathrm{Cr}^{3+} / \mathrm{Cr}$ are $-1.66 \mathrm{~V}$, $0.80 \mathrm{~V},-2.93 \mathrm{~V}$ and $-0.74 \mathrm{~V}$, respectively. The correct decreasing order of reducing power of the metal is
A) $\mathrm{Ag}>\mathrm{Cr}>\mathrm{Al}>\mathrm{K}$
B) $\mathrm{K}>\mathrm{Al}>\mathrm{Cr}>\mathrm{Ag}$
C) $\mathrm{K}>\mathrm{Al}>\mathrm{Ag}>\mathrm{Cr}$
D) $\mathrm{Al}>\mathrm{K}>\mathrm{Ag}>\mathrm{Cr}$
Answer: $\mathrm{K}>\mathrm{Al}>\mathrm{Cr}>\mathrm{Ag}$
Sol:
Higher the value of $E_{\text {red, }}^{\circ}$ stronger is the oxidising power. Thus, the decreasing order of reducing power of the metal is $\mathrm{K}>\mathrm{Al}>\mathrm{Cr}>\mathrm{Ag}$.
