Final answer:
The boiling water overflows because the pot is too full.
Step-by-step explanation:
The correct answer is Option 4: Overflow.
In the given sentence, the boiling water spills over because the pot is too full. When a liquid exceeds the capacity of its container, it overflows. This is what happens when the boiling water spills out of the pot.
In the provided context, the boiling water overflows and causes a potentially dangerous situation, as described in the example passages.