I don't know and do not use this website and this answer is the reason why.
There can be no sensible answer. Litres are a measure of volume, not of mass. Consider a litre of air: what would its mass be? Next consider a litre of water. It will not have the same mass as the air.
By the heating the colligion between atoms will increase so the mass of the air also increases.We cant measure the mass of air but we can measure it with the help of a container.
No, pressure is a measure of the force that air is putting on an object, not a mass. The air itself has mass, but not the pressure.
You need to measure the mass using appropriate equipment. You can measure the volume of a textbook and a container of milk by measuring its linear dimensions and calculating the volume. It is not at all easy to measure the volume of an air balloon. You cannot use displacement of a fluid (water) because when submerged, the balloon would be experiencing water pressure and so would occupy a smaller volume. You cannot measure it by allowing the air to escape and measure that volume of air because that air will no longer be experiencing the pressure exerted by the material (rubber?) of the balloon. I have no answer to this part. Once you have the mass and volume, the density is merely mass/volume.
Mass A rather small mass, such as a dose of medicine or the mass of the air in a jar.
No, millilitres is a measure of volume not mass. You would use milligrams.
Milligram: to measure its mass.
Since air is matter, it does have mass. So adding its mass to the mass of the balloon would cause the balloon to have more mass. Weight is a measure of the pull of gravity on an object and an object with more mass is "pulled" more, so the balloon with air in it would indeed be heavier than a balloon without air.
The most common thing you would measure mass in would be grams and kilograms
You Use Atomic Mass Number
grams which unit would you use to measure the mass of a mouse
Mass is measured using kilograms.