c) 0.1 M Na2SO4 because of the common ion effect.see Sr2(SO4)3 ---> 2Sr+3 + 3 SO4-2 and this will have a common ion effect of SO4-2 and as sodium sulphate is a salt of group 1 therefore it will dissociate 100% and as Stronium sulphate is sparingly soluble and therefore it solubility will decrease.... Solution c) 0.1 M Na2SO4 because of the common ion effect.see Sr2(SO4)3 ---> 2Sr+3 + 3 SO4-2 and this will have a common ion effect of SO4-2 and as sodium sulphate is a salt of group 1 therefore it will dissociate 100% and as Stronium sulphate is sparingly soluble and therefore it solubility will decrease.....