What happens if sodium chloride is added to lead chloride?

1)[cl-] decreases, and [pb2+] increases.

2)[cl-] increases, and [pb2+] decreases.

3)[cl-] increases, and [pb2+] remains the same.

4)[cl-] decreases, and [pb2+] remains the same

The effect of adding sodium chloride will be that of the common ion effect. Under the common ion effect, the solubility of a substance is reduced due to the disturbance of the solubility equilibrium by the addition of an ion that is already present. Therefore, the effect will be:
2) [Cl-] increases (since it is added), and [Pb+2] decreases (due to the common ion effect)

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.