What is the mass of a sample of nacl that needs 732.6 kj of heat to melt completely

Easy definition for atom and atomic mass

Iknow #2 is d. i just need to know why

Great amounts of electromagnetic energy from our sun and other bodies in space travel through space. which is a logical conclusion about these electromagnetic waves? their energy must be very their frequency must be very low these waves can travel without a medium they only travel through a vacuum of space