What best describes the purpose of a controlled experiment

In all living cells dna controls cellular activities by

If you have 5.25 grams of methane (ch4), how many grams of co2 will you produce ?

In the cathode ray tube experiment, j. j. thomson passed an electric current through different gases inside a cathode ray tube in the presence of an electric field. in which two ways did this experiment change scientists’ understanding of the atom?