Refractory materials do not melt sharply at one exact temperature the way a pure metal does, since they are mixtures of several oxides, so their softening happens gradually over a range of temperature. To measure this, a small triangular cone made from the refractory sample is placed next to a row of standard reference cones whose bending behaviour at various temperatures is already known, and the whole set is heated together at a controlled rate in a furnace. As heating continues, the cones start to soften and lean over under their own weight, and the test cone is compared with the standard cones to see which one it matches when its tip finally touches the base plate. The number of the standard cone that bends in step with the test sample becomes its Pyrometric Cone Equivalent value, so it is really a practical stand-in for the refractory's softening temperature, not a measure of density, conductivity or porosity. So the correct choice is option (C).