If atoms are made up smaller parts such as electrons, why are atoms considered the basic unit of matter

Summarize possible ways in which phases of matter could combine to form a solution.

What is the ph of a solution that has a hydrogen ion concentration of 1.0 * 10 -9 m?

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.