30. The solubility of potassium chloride at 20°C is 34.7 g in 100 g of water. The density of the solution is 1.3 g mL–1. What is he w/V percentage of potassium chloride in the solution?
(A) 25.76                                  (B) 32.98                                 (C) 33.49                                (D) 22.56

31. What will be the number of aluminium ions in 0.051 g of aluminium oxide?
(A) 5.0 × 10–4 ions                    (B) 6.0 × 1023 ions                  (C) 12 × 1023 ions                   (D) 6.0 × 1020 ions

32. An ion M 2 + contains 10 electrons and 12 neutrons. What is the atomic number and mass number of element M?
(A) 10, 24                                  (B) 10, 22                               (C) 12, 24                                (D) 12, 22

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