Question

name the principal,which says an orbital can hold only 2 electrons

Answer 1

I think according to the Pauli's Exclusion Principal , an orbit can hold only 2 electrons.
Hope it helps

Answer 2

Hello friend
Here's your answer:

It is called the Duplet rule.
Also Pauli Exclusion Principal is applicable.

Generally, Elements are stable if they have 8 electrons in their valence shell. Which is known as Octet Rule.

But exceptions are there like Hydrogen is Duplet, And some compounds are stable of they have 18 electrons in their valence shell.

Hope my answer helps you.