Q.

In which of the following reaction, the underlined substance has been reduced

1 CO¯+CuOCO2¯+Cu  
2 CuO¯+2HClCuCl2¯+H2O  
3 4H2O¯(g)+3Fe4H2¯(g)+Fe3O4  
4 C¯+4HNO3CO2¯+2H2O+4NO2  

Ans.

(3)

1)  CO+2CO2+4

2)  CuO+2CuCl2+2

3)  H2O+1H20

4)  C0CO2+4

Only in (3), O.N. of hydrogen decreases from +1 to 0 and hence H2O gets reduced to H2.