Pauli exclusion principal says no two electrons can have same set of quantum number since for our distant universe three such electrons exist hence the correct answer for this is 3.
since we have 3 spin quantum number the configuration will be 1s3 2s3 2p2.
A noble gas has all orbital filled, first noble gas will have configuration 1s3 2s3 2p6 which means that its atomic number is 3+3+6 = 12
So, each carbon is bonded to the next carbon with the single bond, Number of unshared electrons left with the terminate carbons are 3 and with the intermediate carbon is 2.
Thus, the two terminate carbon have 3 hydrogen each and the intermediate will have 2.