Answer:
The correct answer is "Red shift"
Explanation:
Blue shift: When the source and observer approach one another, the evident frequency increments or apparent wavelength diminishes. Here the Doppler shift is positive. This is known as blue shift.
Red shift: When the source and observer move away from one another, the clear frequency diminishes or apparent wavelength increments. Here the Doppler shift is negative. This is known as red shift.
