The correct answer is option 'D', J/Kg.

Latent heat is the amount of heat energy required or released during a phase change of a substance, such as melting or vaporization, at a constant temperature and pressure. It is a specific type of heat energy associated with the change in the internal energy of a substance, without a change in its temperature.

There are two types of latent heat: latent heat of fusion and latent heat of vaporization. The latent heat of fusion refers to the heat energy required to change a substance from a solid to a liquid state, while the latent heat of vaporization refers to the heat energy required to change a substance from a liquid to a gaseous state.

The SI unit of latent heat is Joule per kilogram (J/Kg). The Joule is the SI unit of energy, and the kilogram is the SI unit of mass. So, when we express the latent heat in the SI unit, we are essentially referring to the amount of energy required or released per unit mass of the substance during a phase change.

The SI unit of latent heat can be derived by considering the equation Q = mL, where Q is the heat energy required or released, m is the mass of the substance, and L is the latent heat. By rearranging the equation, we get L = Q/m. Since Q is in Joules and m is in kilograms, the SI unit of latent heat is J/Kg.

So, option 'D', J/Kg, is the correct answer for the SI unit of latent heat.