Which is the most important radiation conduction or convection?Explain

convection is more important

In convection there is actual movement of fluid particles for heat transfer whereas in conduction, the particles only vibrate at their position and transfer heat. Due to this kinetic energy transfer in convection is faster than conduction and hence convection is the more efficient way of heat transfer than conduction

temp rises, and expansion

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.