Question

How covalent character of any molecule can be changed?

Answer 1

Answer:

The greater the difference in electronegativity, the more ionic a bond is. The bond with the most covalent character is determined by electronegativities. Smaller difference in electronegativities make a more covalent bond. So you need to decide which molecule has atoms with the most similar electronegativites.

Answer 2

Answer:

On one hand, covalent character increases the bond dissociation enthalpy (i.e., more energy is needed to be put in) and on the other it lowers the melting point of Al2O3 to a value lower then would be expected with perfect ionic bonding.