Fuels and Combustion
A coal with high ash content is undesirable, as

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
All of these
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
It is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber

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Fuels and Combustion
Prime coking coal is always blended with medium or non- coking coal before ear-bonisation

Both A & B
To check against its excessive swelling during heating, which may exert high pressure and damage coke oven walls
Because, it alone produces unreactive coke
Neither A nor B

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