As an electron in a hydrogen atom moves from the second principal energy level to the first principal energy level, the energy of the atom: 1) decreases 2) increases 3) stays the same

Answer is: 1) decreases.

The second principal energy level (n = 2) has higher energy than the first principal energy level (n = 1).

Electrons can jump from one energy level to another, absorbing or emitting electromagnetic radiation with a frequency ν (energy difference of the levels).

When electron jump from higher to lower energy level (shell), it emitting (releasing) energy.

When the electron changes from n=2 (second shell) to n=1 (first shell), the photons are emitted.

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.