Why is kelvin temperature specified in calculations that involve gas?

Lets do some calculations with ideal gas equation using degree centigrade.
Ideal gas equation is as follow,

                                            P V  =  n R T
Now assume you are asked to calculate moles of gas-X at -50 °C. When you solve the equation the answer in your hand will be in - (minus). Now, how can concentration be in negative Means, the degree centigrade scale has failed in terms of Gases.
Now, do the same calculation with Kelvin, -50 °C is equal to 223.5 K. Now you will have answer in positive moles.
Infact, the need for Kelvin scale raised as gases have Kinetic energy at lower temperatures. They need very low temperatures to decrease their K.E. And it was calculated that at -273.5 °C all the motions of gas molecules would freeze (Absolute Zero) and they would have zero kinetic energy. So, this new scale called Kelvin scale was set to study gases. 

What do you mean by that? like the contents? the thc level?