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2.5 mole of O2

Explanation:

From the equation we see that we need 5 molecules of oxygen to react with 2 molecules of C2H2.

This means that 5 moles of oxygen molecules are needed to completely react with 2 moles of C2H2, because a mole is a unit of particle count.

From that we can infer that to react with 1 mole of C2H2 we need half of 5 moles of oxygen - so 2.5 mole of oxygen molecules.

- decrease the number of plants and animals living in the water.

plasma is the state of matter where the substance is ionized and has no definite shape or volume. the fact of being ionized makes the substance a good electrical conductor.