Density, hardness, and luster are three properties of minerals; true or false

Explanation: True

Properties that help identify a mineral in a rock are: color, hardness, luster, crystal forms, density, and cleavage.

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.