Given the balanced ionic equation:
3pb2+ + 2cr ==> 3pb + 2cr3+
what is the number of moles of electrons gained by 3.0 moles of lead ions?
(1) 5.0 mol (3)3.0 mol
(2) 2.0 mol (4) 6.0mol

Answer : The correct option is, (4) 6.0 mol

Explanation :

The given balanced ionic equation is,

In this reaction, lead undergoes reduction and chromium undergoes oxidation.

Half reactions of oxidation and reduction are :

Oxidation :

Reduction :

From the reduction reaction, we conclude that 6 moles of electrons gained by the 3 moles of lead ions.

Hence, the correct option is, (4) 6.0 mole