If you know the name of a substance how can you find out whether or not it is an element

If you already know or have the name of the substance, the simpliest and easiest way to find out whether it is an element or not is to refer to the periodic table and see if the name you have is indicated on the periodic table. If it does, then in that case the substance is an element.

because natural gas is colorless, odorless, and tasteless, distributors add mercaptan (a chemical that smells like sulfur) to give natural gas a distinct unpleasant odor (it smells like rotten eggs). they locate the types of rock that are likely to contain natural gas deposits.