How heavy is a gallon of water

Plz choose one of the compounds from the table and explain how you know the numbers of atoms in your formula. is it possible for two different compounds to be made from the exact same two elements? why or why not? with a limited number of elements (less than 120 are known), does this mean we also have a small number of compounds or do we have a large number of compounds in this world?

Melissa is interested in her family tree and how her family has changed over its many generations. melissa probably more closely resembles

Acontrol during an experiment. might change remains constant does not exist does change