The penny sank when the boy threw the coin into the fountain because the density of the penny is more than the density of the water.
Option B
Step-by-step explanation:
Density is the physical property which relates mass and volume of an object. The equation format for density is given as follows:
![density = \frac {mass} {volume}](https://img.qammunity.org/2021/formulas/physics/middle-school/a1f7yelx4589to7hr31brsr0blebytqmmf.png)
When the density of an object is more obviously it tends to weigh heavier than the lighter objects. Coin being made of metal is naturally heavier and has more density than water. Denser objects tend to sink in liquids less denser than the objects. Hence, coin sinks in water fountain.