7.5毫升0.1摩尔/升硝酸银溶液跟5毫升0.05摩尔/升RClx溶液完全反应，则RClx溶液中

x AgNO3------RClx
-----x-----------1
7.5*0.1------5*0.05
x=3
RClx中x 值是3

Cl离子物质的量浓度是:
5*0.05/(7.5+5)=0.02mol/L

Ag+ + Cl- = AgCl(s)
n(Cl-) = n(Ag+) = 0.1*7.5/1000 = 7.5*10^(-4) mol/L
n(Cl-) = x*n(RClx)=x * 0.05*5/1000 mol/L
x = (0.1*7.5/1000)/(0.05*5/1000) = 0.75/0.25 =3