Question

Which one among the following is the strongest reducing agent?
A.$Ni$
B) $Cu$
C) $Zn$
D) $Fe$

Answer 1

Hint:
A reducing agent is an element or compound which reduces another element or compound and itself gets oxidised by giving out an electron.

Complete step by step answer:
To identify which one is the strongest reducing agent we will consider the standard electrode potential. Before that, we will discuss some points about standard electrode potential. First, when there is a development of potential difference between electrode and electrolyte, it is termed as electrode potential. The potential developed between metal electrode and the solution of its ions at $1M$ concentration and at $1bar$pressure and $298K$, it is termed as standard electrode potential. According to IUPAC, standard reduction potential is now called standard electrode potential. This is quite important as it provides information about a lot of things. If the standard reduction potential of an electrode is greater than zero then, its reduced form is more stable as compared to hydrogen gas and if standard electrode potential is negative then, hydrogen gas is more stable than the reduced form of species. In simpler words more negative the standard electrode potential, less tendency to get reduced (strongest reducing agent) and more positive the standard electrode potential, more tendency to get reduced (strongest oxidising agent). Now we will take all these options one by one.
$$N{i}^{2+}+2e^{-}\to Ni(s)\left(E^0=-0.24V\right)$$
 $$C{u}^{2+}+2e^{-}\to Cu(s)\left(E^0=0.34V\right)$$
 $$Z{n}^{2+}+2e^{-}\to Zn(s)\left(E^0=-0.76V\right)$$
 $$F{e}^{2+}+2e^{-}\to Fe(s)\left(E^0=-0.44V\right)$$
From the above equation we can see that zinc has the highest negative value, so it is the strongest reducing agent followed by iron, nickel and copper, respectively.
So, option C is the correct answer here.

Note:In electrochemical reactivity series, reactivity of metal decreases from top to bottom. Thus Li is the most reactive metal and fluorine is the most reactive non-metal.