Answer: B) in the purification of water Explanation: Alum is a common alum, potassium aluminum sulphate K2SO4.Al2SO43.24H2O which makes colloidally suspended impurities in water such as clay to settle down.

Answer: B) nuclear fission Explanation: In the atom bomb, isotopes of uranium are  disintegrated with the release of a large amount of energy. Hence, the process is nuclear fission.

Answer: A) to make air a moderate supporter of combustion Explanation: If air contained all oxygen and no nitrogen, everything would have burnt off

Answer: C) adding caustic soda Explanation: Water containing caustic soda cannot be used for drinking

Answer: B) calcium bicarbonate Explanation: Temporary hardness is due to the presence of soluble bicarbonates of calcium and magnesium in water. Permanent hardness is due to the presence of sulphates and chlorides of calcium and magnesium.

Answer: B) Law of Definite Proportion Explanation: The Law of Definite Proportion states that the same compound, wherever found or however made, always contains the same elements combined together in the same fixede ratio by weight.

Answer: D) potassium Explanation: Potassium reacts violently with water liberating hydrogen. The reaction is so violent that the liberated hydrogen catches fire.

Answer: C) Phosphorus trisulphide Explanation: The paste applied to the side of a match box is a mixture of phosphorus trisulphide, glass powder (or sand) to cause friction and glue (binding material)