Q.

In acidic medium, K2Cr2O7 shows oxidizing action as represented in the half reaction:

Cr2O72-+XH++Ye2A+ZH2O

X, Y, Z and A, respectively, are                         [2024]

1 8, 6, 4 and Cr2O3  
2 14, 7, 6 and Cr3+  
3 8, 4, 6 and Cr2O3  
4 14, 6, 7 and Cr3+  

Ans.

(4)         

In acidic medium the half reaction is balanced as follows:

(A) Balance atoms undergoing reduction i.e. chromium:

Cr2O72-(aq)2Cr3+(aq)

(B) Balance oxygen using H2O

Cr2O72-(aq)2Cr3+(aq)+7H2O(l)

(C) Balance hydrogen using H+

Cr2O72-(aq)+14H+(aq)2Cr3+(aq)+7H2O(l)

(D) Balance charge using electrons:

Cr2O72-(aq)+14H+(aq)+6e-2Cr3+(aq)+7H2O(l)

On comparing with given reaction we get,

X=14, Y=6, Z=7, A=Cr3+