Answer:
You can add coefficients to the middle of chemical formulas to balance
equations
Step-by-step explanation:
The other three statements are all wrong.
The first statement says you can change the formula of a compound to balance the chemical equation, which is totally wrong.
The third statement is partially correct; you can change coefficients in front of formulas, but you can't change the coefficients in front of symbols. For example, you can't change Ca²⁺ to Ca³⁺ just to balance an equation. These things cannot be changed ever.
The fourth statement is also wrong because conservation of mass is the reason you're balancing the equation in the first place. You balance equations just to make sure there are equal numbers of atoms and/or compound molecules in both sides of the equation. If balancing equations had nothing to do with conservation of mass, then we would not need to balance equations at all.