Final answer:
The red shift observed in the spectral lines from distant galaxies suggests they are moving farther apart, indicating an expanding universe. Light from these galaxies is redshifted because their increasing distance from us stretches the light waves to longer, redder wavelengths. Correct option is b
Step-by-step explanation:
The red shift in the spectral lines of light reaching us from other galaxies implies that these galaxies are moving farther apart from one another. This phenomenon is observed in galaxies that are more than approximately 50×106 light-years away from us.
The red shift, which is a displacement of the spectral lines toward the red end of the visible spectrum, indicates that as galaxies move away from us, their light is shifted to a lower frequency which corresponds to a longer wavelength. This is consistent with the theory of the expanding universe, which suggests that the space between galaxies is increasing, leading to the observation that they appear to be receding from us at significant speeds.