The correct answer is: C. Lime reduces the carbonate hardness and soda-ash removes the non-carbonate hardness.
Hardness in water is caused by the presence of dissolved minerals, mainly calcium and magnesium. These minerals can come from the natural environment, such as limestone and dolomite, or from human activities, such as agriculture and industry.
There are two types of hardness: carbonate hardness and non-carbonate hardness. Carbonate hardness is caused by the presence of calcium and magnesium bicarbonates. Non-carbonate hardness is caused by the presence of calcium and magnesium sulfates, chlorides, and nitrates.
The lime-soda process is a method of water softening that uses lime (calcium oxide) and soda ash (sodium carbonate) to remove both carbonate and non-carbonate hardness.
The lime is added to the water first, and it reacts with the carbonate hardness to form calcium carbonate, which is a precipitate. The soda ash is then added, and it reacts with the non-carbonate hardness to form sodium bicarbonate, which is a soluble salt.
The calcium carbonate precipitate is removed from the water by filtration, and the sodium bicarbonate is then removed by aeration.
The lime-soda process is a very effective method of water softening, and it is used in many industrial and municipal water treatment plants.
Option A is incorrect because it states that only carbonate hardness is removed. This is not true, as the lime-soda process also removes non-carbonate hardness.
Option B is incorrect because it states that only non-carbonate hardness is removed. This is not true, as the lime-soda process also removes carbonate hardness.
Option D is incorrect because it states that lime reduces the non-carbonate hardness and soda-ash removes the carbonate hardness. This is not true, as the lime-soda process uses both lime and soda ash to remove both carbonate and non-carbonate hardness.