Celsius scale is related to kelvin scale by the following equation,
⁰C = K-273
°C = K-273
So as here temperature is given in kelvin, so it can be converted into celsius as follows:
So 20 K = 20K-273 °C
= -253 °C .
So, the 20 K temperature equals to -253 °C.
So , -253 °C is equals to 20 K or 20 K temperature equals to -253 °C.
Fluorine in compounds is always assigned an oxidation number of -1