The correct answer is: A. 0.1 to 0.2 mm.
The laminations of the armature of a D.C. machine are usually 0.1 to 0.2 mm thick. This is because the laminations are used to reduce eddy currents. Eddy currents are induced currents that flow in a closed loop within a conductor. They are caused by the changing magnetic field in the armature. Eddy currents can cause heating and loss of power in the armature. The laminations are made of thin sheets of steel that are insulated from each other. This prevents the eddy currents from flowing from one sheet to another. The laminations are also stacked with a small air gap between them. This further reduces the eddy currents.
The other options are incorrect because they are not the correct thickness of the laminations of the armature of a D.C. machine.