An atom can be excited
a. if it emits a photon.
b. if it collides with another atom or electron.
c. if it absorbs a photon.
d. if it emits a photon or if it collides with another atom or electron.
e. if it collides with another atom or electron or if it absorbs a photon.
Question 2
The time for the Moon to repeat its cycle of phases is equal to
a. its sidereal period.
b. one day.
c. one hour.
d. one year.
e. its synodic period.