Answer:
Statements I and V are true
Step-by-step explanation:
I. Coefficients can be fractions. (TRUE)
Let's suppose we have the following reaction:
Fe + O₂ -------> Fe₂O₃
This can be balanced with round numbers like these:
4Fe + 3O₂ ------->2Fe₂O₃
But if we use simplification of these numbers, dividing by 2 the whole equation we have the following:
2Fe + 3/2O₂ -------> Fe₂O₃
The fraction 3/3 is multiplied by the 2 of the molecule of oxygen: 3/2 * 2 = 3, and with this we'll have the same atoms of oxygen on both sides of equations. Therefore, we can use fractions as coefficients.
II. Subscripts can be fractions. (FALSE)
Subscripts in a chemical reactions represents atoms and these cannot be fractions cause atoms are not represented in a chemical equation with fractions, for example:
Fe + O₂ -------> FeO
We cannot write to balance the equation something like this:
Fe + O1/2 -------> FeO1/2,
The numbers that we use to balance are always written behind the molecules a s coefficients, that's why subscripts are not fractions.
III. Coefficients represent the relative masses of the reactants and/or products. (FALSE)
This is not true either, because the coefficients in a chemical reactions always represent moles of the molecules, and then, with stechiometry we can have an idea of how many moles can be produced in one reaction.
IV. Changing the subscripts to balance an equation can be done only once. (FALSE)
Subscripts represent the atoms of a element or compound as they are in their natural state, so these cannot be changed to balance a equation, we can only use numbers as coefficients and these numbers can be changed.
V. Atoms are conserved when balancing chemical equations. (TRUE)
As we stated in the above four statements, the atoms are conserved basically because the only numbers changing in a chemical equation are the coefficients, therefore, the original atoms in reactions are conserved.