Which of the conditions listed occurs when glassy slag, formed by the burning of fuel oil contaminated with salt water, melts and runs over the furnace wall?

Correct Answer: Option D — Damage to the furnace refractory.

Fuel oil contaminated with salt water produces aggressive sodium and vanadium compounds during combustion. When these molten salt-laden slags run down furnace walls, they act as active fluxes that rapidly dissolve and destroy standard refractory bricks, causing severe structural degradation.