Let's analyze each statement to determine which one is incorrect regarding the geometrical isomers of 2-butene.

Option A: "Cis-2-butene and trans-2-butene are not interconvertible at room temperature."

This statement is correct. Cis and trans isomers of 2-butene are not readily interconvertible at room temperature due to the energy barrier associated with the rotation around the double bond. The double bond ensures rigidity, making interconversion between these isomers difficult without sufficient energy input.

Option B: "Trans-2-butene is more stable than cis-2-butene."

This statement is correct. The trans isomer is more stable than the cis isomer due to reduced steric hindrance. In the cis isomer, the bulkier substituents (methyl groups) are on the same side, leading to increased steric repulsion.

Option C: "Cis-2-butene has less dipole moment than trans-2-butene."

This statement is incorrect. The cis isomer typically has a higher dipole moment than the trans isomer because the substituents on the same side of the double bond create a net dipole moment. In the trans isomer, the dipole moments of the substituents cancel each other out, resulting in a lower overall dipole moment.

Option D: "Cis-2-butene and trans-2-butene are stereoisomers."

This statement is correct. Cis-2-butene and trans-2-butene are indeed stereoisomers because they have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of the substituents around the double bond.

Therefore, the incorrect statement is:

Option C: Cis-2-butene has less dipole moment than trans-2-butene.