Who discovered atomic structure​

This image is an example of a(n) a) atom. b) compound. c) mixture. d) molecule.

A4.86 g piece of metal was placed in a graduated cylinder containing 15.5 ml of water. the water level rose to 17.3 ml. what is the density of the metal. i need the steps of how to solve it to so i can use a formula to work out other problems.

What does a numerical subscript following an element in a chemical formula mean?