Why are sound waves not used to communicate between objects in space?

Because space is a vacuum, so sound can't travel through space do to the fact that there is no molecules to bounce off of.

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.