As you pass a magnet over a blackish-yellow powder on a glass plate, black particles separate from the powder and become attached to the magnet. after a few passes of the magnet over the powder nothing but a yellow powder remains in the glass plate. the original blackish-yellow powder was:

AS given that we have started with a solid powder on a glass plate which appears to be blackish yellow, on passing magnet the black particles separated.

so the black particles are magentic in nature. however the yellow portion of powder is not magnetic or diamagnetic

so its clear that we are able to separate the black and yellow portions by simple physical methods.

If we are able to separate any two substances by simple physical methods then it means that the powder is a mixture and not a compount

the temperature of the gas, in k, not celsius.