Identify the incorrect statement from the following options:

Explanation

Option A is incorrect because refractories used in muffle furnaces are required to have low thermal conductivity to reduce heat loss. Option B is correct since electrical resistivity of refractories falls significantly with rising temperature. Option C is true because well-fired refractories with increased porosity help reduce spalling. Option D is accurate as refractoriness under load is always less than the refractoriness measured without load.