Question

The density of a material varies with temperature.
A. True
B. False

Answer 1

The density of the material is nothing but as mass per unit volume. Since volume is a temperature-dependent quantity, increasing the temperature of the material (with few exceptions) decreases the density of the material by increasing its volume.

Complete answer:
When an object heats up, its mass remains constant (effectively). However, its volume changes, usually.
For the majority of substances, when the temperature increases, the space between particles increases which leads to the object to expand. The object has a larger volume, therefore a smaller density, since volume is inversely proportional to volume. When the temperature gets low, the object will shrink and the density will increase.
This temperature-dependent density effect happens due to the statement “hot air rises”. Hot air at the same pressure is less dense than cold air because the molecules present in material are farther apart. Since the density of it is less, it floats on top of the cold air.
In the case of water in a small region near its freezing point, an increase in temperature will lead the molecules to come out of their hexagonal alignment and on average to move closer together. The volume of the water will decrease, thus water in this narrow temperature range will have its density increase when it gets warmer and decrease when it gets colder. This is a highly important effect and the reason is, as we know, ice floats on liquid water.
Hence, the given statement- density of a material varies with temperature is true.

Therefore the correct option is (A).

Note:
The ratio of change in dimension to original dimensions per degree centigrade is called a coefficient of thermal expansion of the material. The energy related to thermal expansion is heat energy, which always flows from one point of higher temperature to the point of lower temperature by conduction, convection, and radiation.