Which of the following is the least powerful reducing agent in aqueous solution ?

Options

A. Cs
B. Rb
C. Na
D. K

Answer

C

Explanation

The tendency of an element to lose electrons in the aqueous solution is measured in terms of standard reductin potential solution is measured in terms of standard reduction potential, `E^(@)(M^(+)//M)`. Thus, the more negative the `E^(@)`, the higher the tendency of the element of lose electrons, and the stronger the reducing power.
The `E^(@)(M^(+)//M)` of alkali metals becomes more and more negative as we move down the group from Na to Cs. Consequently, the reducing power of alkali metals increases in the same order. Thus, Na with the least negative `E^(@)` is the least powerful reducing agent.