How does critical mass play a role in nuclear reactions?

You may expect bonds between two atoms which each have n covalent lonic metallic hydrogen

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium

What is the amount of energy for a photon that has a 125 cm wavelength