A coal with high ash content is undesirable, as

• A. It is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber
• B. The ash retains the sulphur & phosphorus and thus affects the quality of products in metallurgical furnace apart from increasing the slag volume. Besides, it may fuse and stick to the boiler tubes
• C. All of these
• D. The ash in molten condition gets absorbed in the pores of the refractory lining of the furnace and causes its spalling due to different co-efficient of expansion/contraction of the refractory and the

Answer: (C)