Which statement about boil over is true?

• A. Water at the bottom of the tank boils and causes rapid expansion
• B. Water at the bottom of the tank boils and causes rapid cooling
• C. Water at the top of the tank boils and does not expand
• D. The water never boils in a boil over

Answer: (A)

Boilover happens when water trapped at the bottom of a heated oil mass reaches its boiling point and turns into steam. That phase change creates a huge volume increase in a very short time, so the steam pushes the oil upward and out of the tank in a violent surge. The key idea is that the danger comes from the rapid expansion of boiling water turning into steam, right at the bottom where heat is strongest.

So the true statement is the one describing water at the bottom boiling and causing rapid expansion. The rapid expansion of steam from the boiling water is what drives the oil up and out, which is exactly what boilover is. The other statements don’t fit because cooling isn’t the effect of boiling, boilover isn’t caused by top-water boiling, and water can indeed boil in boilover scenarios.