The mechanical draught _________ with the amount of smoke.

Answer: Option A

Mechanical draught refers to the artificial method of supplying air and removing flue gases using fans in a boiler system.

Smoke formation occurs due to incomplete combustion of fuel, which indicates insufficient air supply.

When the amount of smoke increases, it means combustion is poor and more air is required to burn the fuel completely.

To overcome this, the mechanical draught is increased so that more air is supplied to the furnace, improving combustion and reducing smoke.

Hence, mechanical draught increases with the amount of smoke.