Light is an electromagnetic wave, no matter is wavelength or color.
In this sense, the main characteristic of this type of wave is that it can propagate trhough vacumm, it is not necessary a medium. In addition, electromagnetic waves are transversal waves, this means the electric field oscillates in all normal directions to the direction of wave propagation.
A scalar quantity is defined as the physical quantity that has only magnitude, for example, mass and electric charge. On the other hand, a vector quantity is defined as the physical quantity that has both magnitude as well as direction like force and weight.
No, a machine cannot be 100% efficient. This is due to the movement of the moving parts siding against each other and causing friction. This friction is the one that creates heat and causes wear and tear between moving ports f the machine hence making the machine to decrease in efficiency with time
