Hybridisation

To determine which of the given statements is incorrect, we must analyze each option based on our knowledge of chemical bonding concepts:

1. Hydrogen bonding is stronger than dispersion forces:

   Hydrogen bonds are a type of dipole-dipole attraction that occurs when hydrogen is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine, making it capable of strong intermolecular forces. On the other hand, dispersion forces (London dispersion forces) are the weakest intermolecular forces caused by temporary dipoles. Thus, hydrogen bonding is indeed stronger than dispersion forces. This statement is correct.

2. Sigma bonds are stronger than -bonds:

   A sigma bond ( ) is formed by the head-on overlap of atomic orbitals and is generally stronger than a pi bond ( ), which is formed by the side-to-side overlap of atomic orbitals. Sigma bonds are more stable due to this head-on overlap being more effective than the side overlap of pi bonds. Therefore, this statement is correct.

3. Ionic bonding is non-directional:

   Ionic bonds form due to the electrostatic attraction between ions of opposite charges. Since the force is equal in all directions, ionic bonding is indeed non-directional. Therefore, this statement is also correct.

4. -electrons are referred to as mobile electrons:

   Sigma ( ) bonds involve localized electrons in a specific bond between two atoms, meaning they are not free to move. On the contrary, mobile electrons are typically found in delocalized pi bonds or metallic bonding where electrons can move freely, contributing to electrical conductivity. Hence, this statement is incorrect.

Therefore, the incorrect statement among the given options is: -electrons are referred to as mobile electrons.