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Question:

Which one of the following is the electron deficient molecule?

B2H6

SiH4

C2H6

PH3

Solution:

B2H6 is an electron-deficient molecule because the boron atom has three half-filled orbitals in an excited state. The structure of B2H6 is represented as follows:

In it, two electrons of a B-H bond are involved in the formation of a three-center two-electron bond; these bonds are represented by a dotted line. Hence, option A is correct.