Select all that apply.
all the elements of the halogen family are very reactive because they
readily lose one valence electron
i require only one electron to complete their outer shell
have a high electronegativity
form unstable gas molecules

They require only one electron to complete their outer shell

Explanation:

The elements of group 17 are called halogens. These are six elements Fluorine, Chlorine, Bromine, Iodine, Astatine. Halogens are very reactive these elements can not be found free in nature. Their high reactivity is due to the presence of seven valance electrons. They need just one electron to complete the octet that's why they can not found free in nature. Their chemical properties are resemble greatly with each other. As we move down the group in periodic table size of halogens increases that's way fluorine is smaller in size as compared to other halogens elements. Their boiling points also increases down the group which changes their physical states. i.e fluorine is gas while iodine is solid.

Consider the example of sodium chloride. Chlorine accept one electron from sodium and complete the octet.

The electronegativity of chlorine is 3.16 and for sodium is 0.93. There is large difference is present. That's why electron from sodium is transfer to the chlorine. Sodium becomes positive and chlorine becomes negative ion. Both atoms are bonded together electrostatic attraction occur between them and both get complete complete octet.