If we plot volume of a certain mass of a gas against temperature at constant pressure, we get a straight line intersecting on the negative side at $-273^{\circ }C$ which explains about absolute zero. This graph is known as:

Isobar graph is one in which a line connects points of equal pressure. The Kelvin scale is called the absolute scale of temperature. Absolute zero means the temperature at which molecules stop moving. Kelvin is known as an SI unit of temperature.
Option D is correct.