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