What is meant by controlled variable in chemistry

Each step in the following process has a yield of 70% ch4 + 4cl2 yield ccl4 +4hcl ccl4 + 2hf yield ccl2f2 + 2hcl of 4.50 mole ch4 reacts what is the total amount of hcl produced

When scientists are ready to publish the results of their experimentation, why is it important for them to include a description of the procedures they used?

In ccl4 is there a certain length that the main atom carbon is a certain distance from the chlorine’s?