Question

explain the difference between 2H and h2

Answer 1

2H means two molecules of Hydrogen and $H_{2}$ means one molecule of hydrogen which has 2 atoms

Answer 2

Dude your answer is here I think it helps you H2 is Molecular hydrogen. It is a molecule of hydrogen that consists of two hydrogen atoms bonded together by one single bond (also known as a sigma bond). A subscript also denotes how many of a particular atom is in a molecule, thus H2 has two hydrogens. 2H, on the other hand, denotes two moles of elemental hydrogen.