What are the only things that can change in a valid experiment?

18. use the activity series to predict whether the following synthesis reaction will occur. write the chemical equations for the reaction if it's predicted to occur. (s) + o2(g) -> *note: it is possible.*

In france, grapes are 1.95 euros per kilogram. what is the cost of grapes, in dollars per pound, if the exchange rate is 1.14 dollars/euro? (2.6)

What was bohr’s contribution to the planetary model