A student took four test tubes P,Q,R and S and filled about 8‌ml. of distilled water in each. After that he dissolved an equal amount of Na2SO4 in P,K2SO4 in Q,CaSO4 in R and MgSO4 in S. On adding an equal amount of soap solution and shaking each test tube well, a good amount of lather will be obtained in the test tubes: