Question

If atoms of a halogen nonmetal (Group 17) gains one electron, the atoms the have __.

Answer 1

Hm, this could be more than one option, but gaining electrons makes a negative charge, so

If atoms of a halogen nonmetal (Group 17) gains one electron, the atoms the have "a negative one charge".

Answer 2

Answer : If atoms of a halogen nonmetal (Group 17) gains one electron, the atoms the have (-1) (or, negative) change.

Explanation :

Periods : A row in the periodic table is known as periods.

The common features about the elements of a period are :

Each periods has elements with the same number of electron shells or energy levels or shell.

They transition from metal to noble gas that means they move from metal to non-metal and then non-metal to noble gas.

Groups : A column in the periodic table is known as groups.

The common features about the elements of a same group are :

Each groups has elements with the same number of valance electrons.

The elements in the same group have similar chemical properties.

The elements in the same group have similar physical properties.

The group 17 is a non-metal and known as halogen. The number of valance electrons present in group 17 are 7 valence electrons.

The general electronic configuration of group 17 is:

$ns^2np^5$

As per question, when atoms of halogen gains one electron then the  atoms have (-1) (or, negative) charge and attain stable electronic configuration as noble gas.

For example : The element chlorine belongs to group 17 and the electronic configuration is:

$1s^22s^22p^63s^23p^5$

When chlorine atom gain one electron then the chlorine atom have (-1) charge $Cl^-$.