Which ion will show the least tendency of getting discharged at anode

(A) F?

(B) Cr?

(C) O?

(D) OH?

Dear Student,
Firstly, the species that you have asked in question must be ionic 
i.e F^-,Cr⁺³,O^2- and OH^-
The tendency to get discharged at anode depends on the oxidation potential of the ion (since oxidation takes place at the anode).
From the electrochemical series, we know that the reduction potential of F₂/F^- is maximum i.e $E{°}_{F_2/F^{-}}=2.87 V$
So its oxidation potential, F^-/F₂ will be minimum. Hence Option (A) is the correct answer

Regards