10 g of carbon burns giving 11.2 litres of CO2 at STP. After combustion the amount of unburnt carbon is:

Explanation

We first have to find the moles of CO2. Since the volume of CO2 is given at STP, we can use the molar volume of a gas at STP, which is 22.4 liters per mole. Number of moles of CO2 = Volume of CO2 at STP / Molar volume at STP = 11.2 liters / 22.4 liters per mole = 0.5 moles Now we have to determine moles of carbon burned The balanced chemical equation for the combustion of carbon is: C + O2 → CO2 From the equation, we can see that 1 mole of carbon reacts to produce 1 mole of CO2. Therefore, the number of moles of carbon burned is also 0.5 moles. Now we have to calculate the mass of carbon burned and we can do that by finding the mass of carbon burned using its molar mass, which is approximately 12.01 g/mol. Mass of carbon burned = Number of moles of carbon dioxide * Molar mass of carbon = 0.5 moles * 12.01 g/mol = 6.005 g The initial mass of carbon before combustion was 10 g. To find the amount of unburnt carbon, we subtract the mass of carbon burned from the initial mass: Amount of unburnt carbon = Initial mass of carbon - Mass of carbon burned = 10 g - 6.005 g = 3.995 g Therefore, after combustion, the amount of unburnt carbon is approximately 3.995 grams and if we round it off, its 4g therefore option C is correct.