Q.

The standard electrode potential (M3+/M2+) for V, Cr, Mn and Co are - 0.26 V, - 0.41 V, + 1.57 V and + 1.97 V, respectively. The metal ions which can liberate H2 from a dilute acid are            [2023]
 

1 V2+ and Mn2+  
2 Mn2+ and Co2+  
3 Cr2+ and Co2+  
4 V2+ and Cr2+  

Ans.

(4)

The metal ion for which have less value of reduction potential that (EH+/H2=0) can release H2 on reaction with dilute acid. So, V+2 and Cr+2 reduce H+ to H2.