<u>Answer:</u> The symbol of the ion formed is 
<u>Explanation:</u>
An ion is formed when a neutral atom looses or gains electrons.
- When an atom looses electrons, it results in the formation of positive ion known as cation.
- When an atom gains electrons, it results in the formation of negative ion known as anion.
Electronic configuration is defined as the representation of electrons around the nucleus of an atom.
Number of electrons in an atom is determined by the atomic number of that atom.
The element present in Group 2-A and in period 4 is Calcium (Ca)
Electronic configuration of Ca atom: 
This atom will loose 2 electrons to attain stable electronic configuration similar to Argon element (noble gas)
The electronic configration of 
Hence, the symbol of the ion formed is 
According to Albert Einstein's theory of photoelectric effect, metals will only emit electrons when the incident light has a frequency that is above the minimum or threshold frequency.
So if the frequency of the incident light is less than the threshold frequency then electrons will not be emitted from that metal.
DescriptionIn chemistry an element is a species of atom having the same number of protons in its atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen describes all atoms which have 8 protons. In total, 118 elements have been identified.