(I) B2H6 is an electron deficient hydride. It has 3C−2e−electron deficient bridge bond as follows:
(II) NH3 has lone pair of electrons hence; it is an electron richhydride. (III) NaH is not a covalent hydride. It is an ionic hydride as itbelongs to alkali metal hydride. (IV) YbH2.55 forms an interstitial hydride.
Therefore, statements (I), (II) and (IV) are correct.