A material shows radiation lines when it is heated. Thus, when hydrogen gas is heated inside a discharge tube, only a small amount of radiations is observed because temperature inside the laboratory can be increased to a certain limit. As star (e.g. sun) exhibits a huge temperature, thus hydrogen emits more number of wavelengths in a star as compared to that in laboratory.

Option A. is not correct as spectral lines never depend upon the amount of material taken.

Option C. is not correct as spectral line emission is independent of pressure

Option D. is not correct as spectral lines is also independent of gravitational pull.