An atom has a charge of -2 and 18 electron. What is the element symbol of this atom?
A neutral atom with a charge of -2 means it has gained 2 extra electrons. Since an atom typically has the same number of protons as it does electrons in order to achieve neutrality, we can determine the element symbol by looking at the atomic number.
To find the element symbol, we need to determine the atomic number that corresponds to 18 electrons. The element with an atomic number of 18 is argon (Ar).
Therefore, the element symbol of this atom is Ar (argon).