If the coefficient 2 is placed in front of the product tetraiodine nonaoxide (i4o9), then, how many atoms of each element must be accounted for on the other side of the equation?

8 iodine atoms and 18 oxygen atoms
4 iodine atoms and 9 oxygen atoms
8 iodine atoms and 9 oxygen atoms
9 iodine atoms and 4 oxygen atoms
18 iodine atoms and 9 oxygen atoms

To make sure that an equation is balanced, we need to have the same number of atoms on both sides. If we had only 2(I₄O₉) on one side, then the other side would need to have 8 iodine atoms and 18 oxygen atoms to obey the law of conservation of mass. This can be found by multiplying the coefficient to the subscript followed by the element symbol.

Your correct answer is 8 iodine atoms and 18 oxygen atoms. 

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