What does the big 2 in 2CO2 mean?

Its a coefficient

Explanation:

It has double a normal CO2 has

A number that comes before a compound or molecule e.g 2 in this case is indicating that there are 2 carbon dioxide molecules. Therefore 2CO2 contains: 2×1=2 Carbon atoms.There are four oxygen atoms in the formula 2CO2. The number 2 that is sub-scripted with O determines the number of oxygen atoms, while the number 2 is showing the carbon dioxide atom means how many carbon dioxide is present.

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