Gravity made the egg sink to the bottom of the beaker. The vinegar caused the eggshell to dissolve. The egg was denser than the vinegar. Bubbles appeared on the eggshell.
I gave my students this multiple choice question: When a chicken egg was placed in a beaker of vinegar, bubbles formed on the eggshell. After twenty-four hours, the eggshell is no longer present. Which statement is an observation?

Only one answer is correct among these 4 choices:
- Gravity made the egg sink to the bottom of the beaker.
- The vinegar caused the eggshell to dissolve.
- The egg was denser than the vinegar.
- Bubbles appeared on the eggshell.

Could you tell me which one is correct?

Bubbles appeared on the eggshell.