Question

what is the difference between zinc granules and zinc dust

Answer 1

Zinc granules means small solid crystals of zinc
while zinc dust is a zinc powder.

Hope it's useful.

All the best

Answer 2

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As the particles become finer, more surface of the metal instantly gets exposed for attack by the acid. As a result, the displacement reaction becomes vigorous and much faster with zinc dust. ... If the main purpose of the reaction is to prepare hydrogen gas, it is better to use granules of the metal than its powder.