Which of the following elements always forms covalent bonds?

Options

A. `Pb`
B. `Si`
C. `Al`
D. `B`

Answer

D

Explanation

Because the sum of the first three ionization enthalpies for `B` is so high that it cannot be compensated in the form of lattice enthalpy or hydration enthalpy. Moreover, the hypothetical `B^(3+)` ion will have very high charge density resulting in high polarization of the anion.