How many protons, electrons, and neutrons does an atom with atomic number of 20 and mass number of 40?

What reaction is taking place? 02 + c3h8 = h20 + co2

Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom? some uncharged particles are scattered by a gold foil. all uncharged particles are attracted towards a gold foil. all positively charged particles pass straight through a gold foil. some positively charged particles bounce back from a gold foil.

The chart shows the bid provided by four contractors to complete a job. which contractor is the most cost-effective?