Question

In diborane :

• A. four bridged hydrogen atoms and two terminal hydrogen atoms are present
• B. two bridged hydrogen atoms and four terminal hydrogen atoms are present
• C. three bridged hydrogen atoms and three terminal hydrogen atoms are present
• D. there are no bridged hydrogen atoms in diborane, only hyrogen bonds are present.

Answer 1

The correct option is B two bridged hydrogen atoms and four terminal hydrogen atoms are present

Diborane contains a D2h structure containing four terminal and two bridging hydrogen atoms.

The bonds between boron and the terminal hydrogen atoms are conventional 2-centre, 2-electron covalent bonds.

The bridging hydrogen atoms lie above and below the plane. The two bridges $B-H-B$ bonds are unusual three centred two-electron bonds.

Thus, there are two terminal hydrogen atoms with one boron atom (total 4) and two hydrogen atoms are bridged between two boron atoms.

Hence, the correct answer is option $\text{B}$.