Question

Why are hydrogen and helium alone in a row on the periodic table?

Answer 1

Helium. The position of helium is almost always above neon (which is in the p-block) in the periodic table because it is a noble gas. However, sometimes the position of it is above beryllium because they have similar electron configuration.

Answer 2

The first 2 elements - hydrogen and helium - complete their outer electron shells at 2 electrons instead of the usual 8. So helium has noble gas properties, like e.g. neon, but hydrogen has its own specific properties, neither halogen nor alkali metal. So it's in its own category and placed separately.