The correct option is A A>B>C
For any reaction if Ecell>0, the forward reaction is spontaneous. If Ecell<0, the backward reaction is spontaneous.
For Reaction 1 :
A (aq.)⇌An+ (aq.)+ne−
E∘=+2 V
Oxidation is spontaneous
Reaction 2:
B (aq.)⇌Bn+ (aq.)+ne−
E∘=−3 V
Backward reaction i.e. reduction is spontaneous
Reaction 3:
Cn+ (aq.)+ne−⇌C (aq.)
E∘=+4 V
Forward reaction i.e. reduction is spontaneous
So, tendency of A is the highest for oxidation.
Between reaction 2 and reaction 3:
In reaction 2, E∘ for backward reaction (reduction reaction) is +3V , whereas for reaction 3 E∘ for reduction is +4V
So, C has the highest tendency to get reduced, and thus the least tendency to get oxidised.
Correct decreasing order is:
A>B>C