He, F, and H are unable to serve as central atoms. See explanation for more details.
Work Step by Step
He, F, and H are unable to serve as central atoms. He will not work since it's a noble gas and thus doesn't form bonds with other elements. F would not work well since it only needs one more electron to get an octet, and it is unable to use d orbitals to get an "expanded octet" that wold allow it to be surrounded by more than 8 electrons. Therefore, F is limited to bonding to just one other atom. H would not be suitable since it can only bond to one other atom.