A) The general outer electron configuration of a halogen is:

Here are the answers to the questions:

a) The general outer electron configuration of a halogen is:

$$ns^2 np^5$$

where $n$ is the principal quantum number.

b) The colors of the common halogens are:

• Fluorine ($\text{F}_2$): Pale yellow gas
• Chlorine ($\text{Cl}_2$): Greenish-yellow gas
• Bromine ($\text{Br}_2$): Reddish-brown liquid
• Iodine ($\text{I}_2$): Greyish-black solid (produces purple vapor)