Answer:
Explanation:
An element with atomic number 18 is a noble gas.
The element with atomic number 19 will have one extra electron so it can donate one electron or shed one electron to attain noble gas configuration .
It tends to shed one electron to become positively charged ion . Hence they are electro-positive elements .
Similarly the element with atomic number 17 will have one short electron so it can gain one electron to attain noble gas configuration .
They tend to gain one electron to become negatively charged ion . Hence they are electro-negative elements . They have high electronegativity .
