Which of the following is the electron deficient molecule?

In diborane, 8 covalent bonds and 12 electrons are present. But it requires a total 14 electrons to form bonding. It lacks 2 electron pairs and forms a $3 c-2 e^{-}$bond. Thus $\mathrm{B}_2 \mathrm{H}_6$ is electron deficient.
Related Theory The boron atom is known to be $s p^3$ hybridized and has four hybrid orbitals. The two electrons of the hybrid orbitals in each of the boron atoms form 2 bonds with the Is hydrogen atoms. The two atoms of boron left with that of each unpaired electron orbital and empty orbital forms the two bridging $(B-H-B)$ bonds with that of the two Is hydrogen atoms, is also called as the banana bond.