Given a scientific passage and an answer, generate a question for the given answer.

Passage: Population density is the average number of individuals in a population per unit of area or volume. For example, a population of 100 insects that live in an area of 100 square meters has a density of 1 insect per square meter. If the same population lives in an area of only 1 square meter, what is its density? Which population is more crowded? How might crowding affect the health of a population?. Answer: population density
What is the term for the average number of individuals in a population per unit of area or volume?

Passage: A solute generally lowers the freezing point of a solvent, which is called freezing point depression. For example, spreading salt on an icy road melts the ice. Answer: lowers it
A solute generally does what to the freezing point of a solvent?

Passage: There are other forms of radioactive dating. Rocks, for example, can sometimes be dated based on the decay of 238 U . The decay series for 238 U ends with 206 Pb , so that the ratio of these nuclides in a rock is an indication of how long it has been since the rock solidified. The original composition of the rock, such as the absence of lead, must be known with some confidence. However, as with carbon-14 dating, the technique can be verified by a consistent body of knowledge. Since 238 U has a half-life of solidified about. Answer: radioactive dating
What is the term for dating a rock based on composition decay?