Answer:
a group of unicellular microorganisms
A chemical change is characterized of the formation of new substances or a chemical reaction. There are a number of observations that we can see if this type of change happens. One would be the formation of gas bubbles, this indicates that one of the products is a gas. Another observation would be a formation of a precipitate in the solution, it would indicate that the new solid formed is not soluble in the solution. A permanent color change in the solution would also indicate a chemical change because it may be that the new substance that is formed has its own distinct color when in solution.
Bronze alloy and porcelain dentures
Remember....
mass number= atomic number + number of neutrons
If the mass number is 19 and the atomic number is 9, then the number of neutrons is 19-9 which is 10.
