A marble is attached to a compressed horizontal spring and is then released. Which equation correctly shows the conservation of mechanical energy for this system? mgh=kx^2
1/2mv^2=1/2kx^2
mgh=1/2kx^2
1/2mv^2=kx^2

It is a horizontal spring, so no gravitational potential energy (mgh).

correct equation for spring potential energy is

so out of those options:

however, it seems to me that none of these are correct?

in reality

Total Mechanical Energy

b.transmitters send radio waves, and receivers capture radio waves.