What type of object in the galaxy could you study to investigate whether stars consist primarily of helium or hydrogen

Explanation:

To determine the composition of the star,  scientists takes the help of the atomic physics .  

As Different ions or atoms emits light waves at different combinations of wavelength that is particular of that very atom or element . These light waves are knows as the emission lines and each atom or ion has unique emission spectra which allows them to distinguish which kind of element light is sent out from the star and hence distinguish whether the star is made up of hydrogen or helium .  

d. they are naturallyoccuring inorganic fuels like coal and petroleum.

because the two particles have an equal charge, the charges will cancel out and give the atom an overall charge of 0. so, if at atom has 35 protons in the nucleus, we could expect it to have 35 electrons orbiting that nucleus.