In the process 

 (in aq medium), initially there are 2 mole I₂ & 2 mole I^- . But at equilibrium, due to addition of AgNO_3(aq), 1.75 mole yellow ppt is obtained. K_C for the process is (V_flask=1 dm³) nearly

Initial moles of I₂ = 2

Initial moles of I ^- = 2

Volume of the vessel = 1 litre

Yellow ppt formed by the addition of AgNO₃ is AgI

Number moles of AgI precepitated at equilibrium = 1.75

number of moles of I^- at equilibrium = 1.75

Number of moles of I^- reacted = (2 -1.75) = 0.25

According to stoichiometry

1 mole of I₂ reacts with 1 mole of I^-

x mole of I₂ reacts with 0.25 moles of I^-

Similarly moles of 

formed due to the reaction of 0.25 moles each of I₂ & I^- will 0.25

Initial moles	2	2		-
Moles at equilibrium	(2 - 0.25)	(2 - 0.25)		0.25
Equilibrium concentration