Solid is more dense than a gas.

• A. Gas is more dense than solid
• B. Solid is more dense than gas
• C. Liquids are always the least dense
• D. Density does not vary with pressure

Answer: (B)

Density is a measure of how much mass fits into a given volume. In a solid, particles are packed tightly with very little empty space, so a sample has a large mass in a small volume. In a gas, particles are far apart and move freely, so the same amount of gas takes up a much larger volume and has a much smaller density under ordinary conditions. That’s why solids are typically more dense than gases. The other ideas don’t fit as well: a gas being more dense than a solid isn’t the usual case, liquids aren’t always the least dense, and gas density changes with pressure and temperature (solids aren’t as easily compressed, so their density changes less).