In balancing chemical equations, what are the rules concerning coefficients and subscripts?

The coefficients must be whole numbers and if the coefficient is 1, then don't write a number in, it is already assumed that the coefficient is 1 when you don't write a number. You can change the coeffecients as many times as you want as long as the equation is still balanced. after balanced, it's best to simplify the coefficients if you can.

For subscripts, they should never change when you have an equation fully written out. the subscripts tell us how much of each element is required for the specific chemical and if they're changed then you could risk unbalancing the equation or balancing the wrong chemical.