Lumen

1.a nuclear reaction in which the nucleus of atoms are joined
2.the science dealing with the conversion of heat and energy
3.the energy of heat
4.a nuclear reaction in which a nucleus of atoms is divided
5.the basic unit of measure for light

The correct answer is 5. A lumen is the basic unit of measure for light, which refers to the total amount of light emitted by a source in all directions. It is used to quantify the brightness or intensity of light in a given area.

Lumen is the basic unit of measure for light.