When a liquid is heated, what typically happens to its density?

• A. The density first increases, then decreases.
• B. The density decreases because the liquid expands.
• C. The density increases because the liquid contracts.
• D. The density remains unchanged.

Answer: (B)

Verified step by step guidance

1. Recall the definition of density, which is mass divided by volume: \(\text{density} = \frac{\text{mass}}{\text{volume}}\).
2. Understand that when a liquid is heated, its temperature increases, causing the liquid molecules to move more vigorously and generally spread apart.
3. As the molecules spread apart, the volume of the liquid increases (the liquid expands). Since the mass remains constant, an increase in volume leads to a decrease in density.
4. Therefore, heating a liquid typically causes its density to decrease because the volume increases while the mass stays the same.
5. This explains why the correct answer is: 'The density decreases because the liquid expands.'