Which is not a pure substance? Ice cream
Ice cream

Carbon Dioxide
Carbon Dioxide

Ice cream is not a pure substance. A pure substance consist of 1 particular element or compound only.

Explanation:

Ice cream is a mixture of substances but carbon dioxide is a compound of carbon and oxygen

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !