The incorrect statement among the following is:

1. Paramagnetic substances are weakly attracted by magnetic field.
2. Ferromagnetic substances cannot be magnetised permanently.
3. The domains in antiferromagnetic substances are oppositely oriented with respect to each other.
4. Pairing of electrons cancels their magnetic moment in the diamagnetic substances.

HINT: Ferromagnetic substances can be permanently magnetized. 
Explanation:
Ferromagnetic substances can be magnetized by applying a magnetic field to them and magnetic properties persist within it even after removal of the magnetic field.
Write three properties of ferromagnetic materials class 12 physics CBSE
Hence, option (2) is the correct answer.