The change in temperature of a body is $50^{\circ }\text{C}$, The change in temperature on the Kelvin scale is

A change or interval of temperature on the Celsius scale is exactly equal to the change on the Kelvin scale because the size of a degree is identical on both scales:
$$\Delta T(\text{K})=\Delta T{(}^{\circ }\text{C})$$
Given $\Delta T=50^{\circ }\text{C}$, the change in temperature on the Kelvin scale is simply $50\text{K}$.