Scale formation in a flash-type evaporator is usually found in the __________.

Correct Answer: Option C — tubes of the salt water feed heater

Flash-type evaporators utilize a salt water feed heater to raise the temperature of the incoming seawater before it enters the flash chamber. Because this heater operates at the highest temperatures in the system, it is the primary location for calcium carbonate and magnesium hydroxide scale formation, necessitating regular chemical treatment.