Question

What is the difference between magnesium powder and magnesium ribbon

Answer 1

The powder form has a much larger surface area per unit weight of magnesium than the ribbon form ,so while the ribbon will react rapidly with the acid, the powdered form will be nearly explosive and dangerous in that a great amount of hydrogen gas and heat will be formed in a fraction of a second.
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Answer 2

The magnesium powder has a larger surface area than the ribbon so when it reacts with substances like sulphuric acid, it creates a much more explosive and dangerous reaction, whilst the ribbon still reacts very quickly but is less explosive.
Hope this helps :)