(a) The solubility of sodium chloride in water increases with rise in temperature while that of lithium carbonate decreases. Assign reason.
(b) Water containing 88.8% oxygen and 11.2% hydrogen is often used as a fire extinguisher. Can a mixture containing the two gases in the same ratio by mass be used for extinguishing fire ?
(c ) The melting point of a solid when determined experimentally comes out to be `160^(@)C`. But its actual melting point as given in standard books is `150^(@)C`. Predict the nature of the solid.

Explanation

(a) When sodium chloride is dissolved in water, the process is endothermic in nature. This means that heat energy is absorbed in the process. Therefore, solubility increases with rise in the temperature. In case of lithium carbonate, the process of dissolution is exothermic. This means that heat is evolved in the process. Therefore, its solubility in water decreases with rise in temperature.
(b) No, it cannot be used. Actually, in water the two elements are chemically combined with each other. They therefore, lose their identify. But in the mixture, no chemical combination between hydrogen and oxygen has taken place. Even water cannot be formed on mixing the gases. Therefore, the mixture does not extinguish any fire.
(c ) Since the experimentally determined melting point of the solid is more than the standard value of the melting point, this means that the solid is not in pure state. It has some impurities present. Please note that the purity of a solid can be determined by finding its melting point and comparing it with the standard value.