Question

Which of the following explains why elements in column 17 (the halogens) are very reactive?
Their atoms contain three energy levels.
Their atoms need only one electron to complete their outer energy level.
Their atoms have large masses.
Their atoms contain the same number of protons as electrons.

Answer 1

their atoms need only one electron to complete theirouter energy level

Answer 2

Answer: Halogens are very reactive because their atoms need only one electron to complete their outer energy level.

Explanation :

The elements of group 17 are called halogens. They are highly reactive of all other elements. Their general electronic configuration is $ns^2\ ns^5$.

Halogens have 7 valance electron in their outermost shell. They need only one electron to complete their orbits. So, they have a tendency to gain one electron from other atoms.

So, the correct option is (C) " Their atoms need only one electron to complete their outer energy level ".