Define density.

Density is a measure of how much mass is contained in a given volume. It is calculated as mass divided by volume.

where $\rho$ is density, $m$ is mass, and $V$ is volume.

When matter is heated, its particles gain kinetic energy and spread out, causing the volume ($V$) to increase. Since density is mass divided by volume ($\rho = \frac{m}{V}$), and the mass ($m$) remains constant, an increase in volume leads to a decrease in density.

In a layered liquid system, the liquid with the highest density will settle at the bottom, while less dense liquids float on top. Based on the diagram, the lowest layer in the container (which is below the white grape juice) has the highest density.

The layer with the highest density is the bottom layer.