A student takes four test tubes marked P, Q, R and S of 25 mL capacity and fills 10 mL of distilled water in each. He dissolves one spoonfull of four different salts in each as: KCl in P, NaCl in Q, CaCl2 in R and MgCl2 in S. He then adds about 2 mL of a sample of soap solution to each of the above test tubes. On shaking the contents of each of the test tubes, he is likely to observe a good amount of lather (foam) in the test tubes marked________.
(A) P and Q (B) R and S
(C) P, Q and R (D) P, Q and S
