What is the difference between 2H and H2?
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. It should be noted that elemental hydrogen is not bonded to anything.