A student takes about 4 ml of distilled water in four test tubes marked P, Q, R, and S. He then dissolves in each test tube an equal amount of various salts, viz. sodium sulphate in P, potassium sulphate in Q, calcium sulphate in R, and magnesium sulphate in S. After that, he adds an equal amount of soap solution to each test tube. On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tube marked:<p></p>

A student takes about 4 ml of distilled water in four test tubes marked P, Q, R, and S. He then dissolves in each test tube an equal amount of various salts, viz. sodium sulphate in P, potassium sulphate in Q, calcium sulphate in R, and magnesium sulphate in S. After that, he adds an equal amount of soap solution to each test tube. On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tube marked:

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