E MULTIPLE-CHOICE QUESTION Why are hot fluids less dense than cold fluids? An increased temperature causes the molecules to spread apart. An increased temperature causes the molecules to get closer together. An increased temperature causes the molecules to become equally spaced.

## Step 1<br />The problem is asking why hot fluids are less dense than cold fluids. The term "density" refers to the mass per unit volume of a substance. <br /><br />## Step 2<br />When a fluid is heated, the molecules gain kinetic energy and move faster. This increased movement causes the molecules to spread apart, which increases the volume of the fluid.<br /><br />## Step 3<br />Since the mass of the fluid remains constant, but the volume increases, the density of the fluid decreases. This is because density is defined as mass divided by volume. <br /><br />## Step 4<br />Therefore, the correct answer is that an increased temperature causes the molecules to spread apart, which in turn decreases the density of the fluid.