How much thickness is necessary for amalgam for resistance?

The appropriate thickness for amalgam for resistance is not explained based on the given options. However, based on standard practice and research, the ideal thickness for amalgam restorations is 1.5-2mm. Options A and D fall short of this range and may not provide sufficient strength and resistance against fracture or wear. Option C is too thick and may lead to difficulties during placement and risk of overhangs. Therefore, option B remains the most suitable and commonly used thickness for amalgam restorations.