.50 M KCl because 5% is the same as .05, which makes the .50M more concentrated.
The different school faucets (frequently and infrequently used) are the manipulated or independent variable. The exact school faucet being tested is chosen (in a sense, manipulated) to test a particular effect or in this case, the presence of <span>more chemical impurities.</span>
Formation of hydrates is considered to be a chemical change.
