Which among the following is a unit of measurement that describes the rate at which the universe is expanding?

Hubble constant

The correct answer is option 4. Hubble constant.

The unit of measurement that describes the rate at which the universe is expanding is Hubble constant.

The Hubble constant, denoted by \(H_0\), is a measure of the rate at which the universe is expanding. It represents the velocity at which galaxies are moving away from each other due to the expansion of space. The current best estimate for the value of the Hubble constant is around 70 kilometers per second per megaparsec (km/s/Mpc). It is named after the American astronomer Edwin Hubble, who first observed and provided evidence for the expanding universe.