Answer:
1. Argon (Ar).
2. Lithium (Li).
3. Oxygen (O).
Explanation:
1. We just have to find the element whose number is 18. This element is Argon (Ar).
2. We just have to find the element whose number is 3, because in a neutral atom, the amount of electrons is equal to the number of protons. This element is Lithium (Li).
3. We just have to find the element with an atomic mass of 16.0 amu. This element is Oxygen (O).
