Correct Answer - 4
`E_(Cr^(3+)//Cr^(2+))^(0)=-0.41V, E_(Mn^(3+)//Mn^(2+))^(0)=+1.57V,E_(Fe^(3+)//Fe^(2+))^(0)=+0.77 V,E_(Co^(3+)//Co^(2+))^(0)=+1.97 V`
SRP value normaly increases from left to right in the period of d-block element. Some SRP value are exceptionally higher due to stability of product ion. For e.g. `E_(Mn^(3+)//Mn^(2+))^(0)=+1.57V,E_(Co^(3+)//Co^(2+))^(0)=+1.97V`.