Emission of light from an atom occurs when an electron
drops from a higher to a lower energy level
jumps from a lower to a higher energ) level
moves within its atomic orbital
falls into the nucleus

Emission of light occur from an atom when electron drop from a higher energy level to lower energy level.

Explanation:

Excitation:

When the energy is provided to the atom the electrons by absorbing the energy jump to the higher energy levels. This process is called excitation. The amount of energy absorbed by the electron is exactly equal to the energy difference of orbits.

De-excitation:

When the excited electron fall back to the lower energy levels the energy is released in the form of radiations. this energy is exactly equal to the energy difference between the orbits. The characteristics bright colors are due to the these emitted radiations. These emitted radiations can be seen if they are fall in the visible region of spectrum.

The answer is:

drops from a higher to a lower energy level

water at room temperature is flowing through a pipe with pressure taps located 10 ft apart along one section of the pipe, which are connected to a mercury (s=13.6) manometer.