A student measured the pH values of four solutions P, Q, R and S as 10, 6, 0 and 12 respectively. The solution which is the most acidic is likely to be the solution :
(1) P
(2) Q
(3) R
(4) S

Correct answer: (3) R

Explanation: pH scale ranges from 0-14, acids lie between 0 to 7,  pH = 7 is neutral and bases lie between pH 7.1 to 14. Lower the value of pH stronger will be the acid, hence the solution having pH = 0 (R) is the strongest acid.