Solution :
Comparing the solubility of silver chromate for the solutions :
----- Less soluble than in pure water.
----- Less soluble than in pure water.
----- Similar solubility as in the pure water
----- Similar solubility as in the pure water
The silver chromate dissociates to form :
When 0.1 M of 
is added, the equilibrium shifts towards the reverse direction due to the common ion effect of 
, so the solubility of 
decreases.
Both 
and 
are neutral mediums, so they do not affect the solubility.
It is approximately 10 ^ -10
To solve for the number of moles, we simply have to use the Avogadros number which states that there are 6.022 x 10^23 molecules per mole. Therefore:
number of moles = 6.67 X 10^40 chlorine molecules / (6.022 x 10^23 molecules / mole)
number of moles = 1.108 x 10^17 moles
(2) three fewer valence electrons is your answer.
