When x grams of carbon are heated with y grams of oxygen in a closed vessel, Why no solid residue is left behind?

When x gm carbon is burnt with y gm oxygen in a closed vessel, no residue is left behind. Which of the following statement is correct regarding the relative amounts of oxygen and carbon?

A mixture of 2 mol of carbon monoxide and 1 mol of oxygen in a closed vessel is ignited to get carbon dioxide , then

An organic compound whose empirical and molecular formula are same, cantains 20% carbon, 6.7% hydrogen, 46.7% nitrogen and the rest oxygen. On heating it yields ammoia, leaving a solid residue. The solid residue gives a voilet colour with dilute solution of alkaline copper sulphate. The organic compound is