Are atoms that carry an electric charge.
a. colloids
b. electrolytes
c. nonelectrolytes
d. ions

Ions are atoms that carry an electric charge.

Explanation:

An ion is an atom or molecule that does not have a neutral electric charge. In other words, ions are atoms or groups of atoms that have an electric charge. Ions with a positive charge are called cations. Those with a negative charge are called anions.

Ionization is the formation of electrically charged molecules or atoms. Atoms are electrically neutral. The loss of one or more electrons from a neutral atom forms a cation. Conversely, an anion is an ion whose net charge is negative due to an increase in the number of electrons.

Cations and anions are usually represented with the symbol of the corresponding atom or group of atoms and the symbol "+" or "-", respectively. If the number of electrons gained or lost is greater than one, this is indicated by the corresponding number.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.