At 298 K the standard reduction potentials for the following half reactions are given as
$\large Z{n^{2 + }}_{\left( {aq} \right)} + \,2{e^ - }\, \to \,Z{n_{\left( s \right)}};\, - 0.762\,V$
$\large C{r^{3 + }}_{\left( {aq} \right)} + \,3{e^ - }\, \to \,C{r_{\left( s \right)}};\, - 0.740\,V$
$\large 2{H^ + }_{\left( {aq} \right)}\, + \,2{e^ - }\, \to \,{H_{2\left( g \right)}};\, - 0.00\,V$
$\large F{e^{3 + }}_{\left( {aq} \right)}\, + \,{e^ - }\, \to \,F{e^{2 + }}_{\left( {aq} \right)};\, + 0.770\,V$
The strongest reducing agent is

Easy

Solution

$E_{{M^{ + n}}_{\left( {1M} \right)}/M}^o\,value\,\,is\,\,low$
Right hand species readily undergoes oxidation and is strong reducing agent.
$E_{{M^{ + n}}_{\left( {1M} \right)}/M}^o\,value\,\,is\,\,high$
Left hand species readily undergo reduction and is strong oxidising agent
Among the given SRP values Zn electrode is having lowest value. The right hand species Zn is readily undergoing oxidation and is strong reducing agent.
Order is
$Zn > Cr > {H_2} > F{e^{ + 2}}$
Among the given SRP values Fe electrode is having highest value. The left hand species Fe⁺³ readily undergoes reduction and is strong oxidizing agent.
Order is
Fe⁺³ >H⁺ >Cr⁺³ >Zn⁺²

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