If a laser operating at a wavelength of 488 nm and a power of 123.0 mW is turned on for 18.73 minutes, how many photons has it emitted?

3.39e+20

Explanation:

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.