Question

The powerful reducing agent in aqueous medium is:
A.${\text{Cs}}$
B.${\text{F}}$
C.${\text{Cl}}$
D.${\text{Li}}$

Answer 1

We must have the knowledge about properties of metals and the electrochemical series. There is a definite series that is obtained from the experimental data. It is based on the standard reduction potential values, higher the standard reduction value higher is the reducing character.

Complete step by step answer:
Electrochemical series defines the arrangement of elements according to their respective electrode potential value. They are either arranged in increasing or decreasing order in electrochemical series
The values of electrode potential are calculated using standard hydrogen electrodes as reference. The potential value it shows is basically standard reduction potential. Metal always loses electrons and hence are electropositive in nature. Higher the standard reduction potential of an element, higher will be its tendency to reduce other elements and oxidize itself hence it will lose electrons readily and will be a good metal. So if the electrochemical series is arranged in increasing order of the standard electrode potential then metals will be on the bottom half of the series, below hydrogen. Hence according to the electrochemical series ${\text{Li}}$ is a powerful reducing agent.
Moreover we know that among the given options only lithium is metal and can donate electrons easily and hence reduces other and is a better reducing agent. Others are halogens that have non metallic character and have a tendency to accept electrons. No doubt cesium is also a metal but electrode potential is lesser than lithium due to various factors.
Some of the applications of Electrochemical Series are: To check the Oxidising and Reducing Strengths, for calculation of standard emf of a cell, to predict the spontaneity of Redox reaction.

Hence the correct option is D.

Note:
Electrode potential is the ability of an element to lose or gain electrons when it is placed in the solution of its own ion. An element can even lose an electron or gain an electron, it depends on the nature of the element. A redox reaction is a reaction in which oxidation and reduction occurs simultaneously.