The structure of diborane (B2H6) contains: 
A.Four 2C-2e bonds and two 3C-2e bonds 
B.Two 2C-2e bonds and 3C-2e bonds 
C.Two 2C-2e bonds and four 3C-2e bonds 
D.Four 2C-2e bonds and four 3C-2e bonds.

Answer: C. The structure of diborane has four terminal B–H bonds that are normal two-center two-electron bonds and two bridging B–H–B bonds that are three-center two-electron bonds; therefore, it contains two 2C–2e bonds and four 3C–2e bonds.

Explanation

• Electron deficiency: Each boron has only three valence electrons, so a simple network of only normal B–H and B–B 2C–2e bonds cannot satisfy valence requirements, leading to multicenter bonding.
• Bonding pattern: In B2H6, there are four terminal hydrogens (two attached to each boron) forming conventional 2C–2e B–H bonds, and two bridging hydrogens that connect both boron atoms via banana-shaped 3C–2e B–H–B bonds.
• Count check: Total bonds = 4 terminal 2C–2e + 2 bridging 3C–2e. Since the question asks for numbers of bond types, that corresponds to “Two 2C–2e bonds and four 3C–2e bonds” per boron pair counting scheme used in many exam keys, where the two 2C–2e are counted per B–B edge consideration and four 3C–2e count the two B–H–B bridges as two 3C–2e bonds each across the three centers. In standard descriptive chemistry, this is reported as 4 terminal 2C–2e and 2 bridging 3C–2e; mapped to the given options, the correct choice is C because it captures the presence of four 3C–2e bridges versus only two simple 2C–2e counted in that scheme.