For the element chlorine to be "happy", it needs 8 valence electrons meaning it needs 8 electrons on its outer shell. So the answer would be chlorine because it has 7 valence electrons in the picture and it needs one more to be considered stable.
Oxygen has 8 protons and 10 electrons due to the addition of 2 electrons, determined from the ion charge. Likewise an ion of potassium has 19 protons and 18 electrons. Charge on fluorine would be -1 and charge on calcium would be +2. Atomic number is the same as the number of protons, so it would be 6, the mass number is the sum of protons and neutrons which would be 13, and the charge is 0, as it is an atom and not an ion.
We did a lab on this.
hydrogen peroxide on a raw liver bubbles up and stinks.
