The spectrum of a distant star contains sodium lines that are offset from their normal position, as shown. what is the most likely explanation?
sodium spectra
a. the star is relatively hot.
b. the star is relatively cool.
c. the star is moving rapidly toward us.
d. the star is moving rapidly away from us.

C. The star is moving rapidly toward us.

Explanation:

The sodium lines are blue shifted in star's spectrum. Doppler's effect for light describes that the apparent wavelength is different than the source due to relative motion between the source and the observer.

A red shift means wavelength shift towards red i.e. longer wavelength is obtained than emitted by source. This happens when the source and observer move away from each other.

A blue shift indicates that source and observer are moving closer because shorter wavelength is obtained than emitted by source.