The green and black symbols refer to atoms, that make up the molecule of water, more specifically you can say that the 2 Hydrogen atoms are the black ones found outside, while the central atom, that is also green would be oxygen.
Answer: By looking at the periodic table, you will see that Fluorine has 9 protons. Since the number of electrons equal the number of protons, Fluorine has 9 electrons as well. Meanwhile, it's mass number of 19, minus 10 neutrons, gives you 9 protons or electrons. Hence, the atom would be Fluorine.
Explanation:
Because atoms are the small and can't be seen by your eyes. It is so small that scientists need to use a model. A model help scientists study things. So, scientists needs to study atoms using models.