Fuels and Combustion
The maximum adiabatic flame temperature in air as compared to that in pure oxygen is

Either lower or higher, depends on the type of fuel
Same
Much higher
Much lower

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

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

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