Question

Ne2 molecule does not exist .why?

Answer 1

because it is a noble gas and noble means non reactive. it has its outermost shell completly filled with electrons and don't needs to react with another atom

Answer 2

Neon molecule does not exists because it has no bond order and cannot exist.

Explanation:

Neon is denoted by Ne which is noble gas. Noble gases are non-reactive by nature.

The outermost shell in Ne element is fully filled with electrons where the electron is 10 in number. This means that $Ne_2$ will have 20 electrons. This is why it does not need to react with any other atom and so has no bond order and cannot exist.

According to the "Molecular Orbital Theory", only those molecules exists that have a positive bond order and molecules with no bond or negative bond order cannot exist.