The states that control is enhanced by concentrating on the exceptions to, or significant deviations from, the expected result or standard.

The principle of exception is the managerial principle that states that control is enhanced by concentrating on the exceptions to, or significant deviations from, the expected result or standard.
This also refers to the fact that only what is important in a budget or a plan is shown to the manager, while the rest is excluded. 

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table