The nucleus of a hydrogen atom consists of A. 1 proton only B. 1 proton + 2 neutron C. 1 neutron only D. 1 electron only

The correct answer is A. 1 proton only.

A hydrogen atom consists of a single proton in the nucleus and a single electron orbiting the nucleus. The proton has a positive charge, the electron has a negative charge, and the nucleus is held together by the strong nuclear force.

Option B is incorrect because a hydrogen atom has only one proton in its nucleus, not two protons.

Option C is incorrect because a hydrogen atom has no neutrons in its nucleus, not one neutron.

Option D is incorrect because a hydrogen atom has one electron in its orbit, not one electron in its nucleus.