Why can density use as a means identification?

How have the greenhouse gasses increased from the year 2000 to 2018

While in europe, if you drive 125 km per day, how much money would you spend on gas in one week if gas costs 1.10 euros per liter and your car’s gas mileage is 32.0 mi/gal? assume that 1 euro=1.26 dollars

Rank the four gases (air, exhaled air, gas produced from from decomposition of h2o2, gas from decomposition of nahco3) in order of increasing concentration of co2