Question

Four alkali metals $A,B,C\text{and}D$ are having respective standard electrode potential as $-3.05,-1.66,-0.40$ and $0.80V$.
Which one will be the powerful reducing agent?

• A. A
• B. B
• C. C
• D. D

Answer 1

The correct option is A A

Standard reduction potentials (SRP) of the half cell electrodes are calculated and arranged in a series of increasing order which is known as electrochemical series.
The standard electrode potential of $H^{+}/H_2$ couple is zero.

Here, a negative $E^0$ signifies that it has high tendency to get oxidised and the redox couple is a stronger reducing agent than the $H^{+}/H_2$ couple.

A positive $E^0$ signifies that it has high tendency to get reduced and the redox couple is a stronger oxidising agent than the $H^{+}/H_2$ couple.

$A^{+}\left(aq\right)+e^{-}\to A\left(s\right);E^0=-3.05V$
$B^{+}\left(aq\right)+e^{-}\to B\left(s\right);E^0=-1.66V$
$C^{+}\left(aq\right)+e^{-}\to C\left(s\right);E^0=-0.40V$
$D^{+}\left(aq\right)+e^{-}\to D\left(s\right);E^0=0.80V$


More negative the standard reduction potential greater is the tendency to lose electrons and hence, metal A is the most powerful reducing agent.