Concept:Calcium carbonate (
CaCO3) can seal soil pores in a fish pond, thereby checking seepage and loss of water.
Explanation:Sandy or porous pond beds lose water easily through seepage.
Applying calcium carbonate to the pond bottom helps fine clay particles to settle and block these soil pores.
This reduces the rate of water loss and helps maintain the pond water level.
The other options are not suitable for sealing pond soil.
SO2 (sulphur (IV) oxide) is an acidic gas, ammonium sulphate is mainly a fertiliser, and potassium hydroxide is a strong alkali.
None of these are used for sealing pond beds.
Thus, calcium carbonate is the best choice for this purpose.
Answer:C. Calcium carbonate