Chemical Process
Viscosity index improver (like polystrene or polyisobutylene) is added to lubricant to

Increase the variation in its viscosity with temperature
Increase its viscosity
Reduce its viscosity
Reduce the variation in its viscosity with temperature

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Chemical Process
Pitch (a product of coal tar distillation) is always mixed with creosote oil, when it is to be burnt in a burner, because

Tar neutralises the residual acids present in pitch
It reduces viscosity and imparts fluidity for its transportation through pipelines at economic pressure drop
Its calorific value is very less
All of these

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