A student measured the pH values of four solutions A, B, C and D which were found to be 4, 1, 13 and 11 respectively. Which of the following statements are correct about these solutions?
(a) A is strong acid and B is weak acid
(b) B is strong acid and D is weak base
(c) D is strong base and C is weak base
(d) C is strong base and A is weak acid
(1) (a) and (b)
(2) (b) and (c)
(3) (c) and (d)
(4) (b) and (d)

Correct answer: (4) (b) and (d) 

Explanation: pH scale ranges from 0-14. Acids range from 0-6.9 and bases range from 7.1-14. The lower the value of pH stronger the acid or the higher the value of pH stronger will be the base. So, A and B are acids but the pH of B is less than the pH of A, hence B is a stronger acid than A. C and D are the bases but the pH of C is more than the pH of D, hence C is a stronger base than D.