The hardness of the bone tissue is due to the phosphates and carbonates of ___________ and ___________.

Q. Assertion (A): Hardness of water is removed by treatment with sodium carbonate.
Reason (R): Sodium carbonate reacts with soluble magnesium and calcium chloride to form water soluble compounds.

Q. Which of the following pair of elements represents a mole ratio of 1 : 1 ?
(a) 10 g of calcium and 12 g of magnesium
(b) 12 g of magnesium and 6 g of carbon
(c) 12 g of carbon and 20 g of calcium
(d) 20 g of sodium and 20 g of calcium

Q. The elements whose oxides can turn litmus solution blue are:
(a) carbon and sulphur
(b) sodium and carbon
(c) potassium and magnesium
(d) magnesium and sulphur

Q. In a permutit, the calcium and magnesium ions of hard water are exchanged by:

Q. In the neighbourhood of your school, hard water required for an experiment is not available. Select from the following groups of salts available in your school, a group each member of which, if dissolved in distilled water will make it hard :

(a) Sodium chloride, calcium chloride

(b) Potassium chloride, sodium chloride

(c) Sodium chloride, magnesium chloride

(d) Calcium chloride, magnesium chloride