This depends on the country yo live in. Some countries measure it in gallon and some in liters. 1 gallon = 3 liters.
Depends where you live. Where I live it would be measured in US Gallons.
You should use litres.
The volume of the bottle would be in litres.
To reduce the amount of gasoline they use.
You would use Volume.
I would think one that holds gasoline and doesn't leak would be a proper replacement.
Gasoline is NOT good for a tree. It would kill it "IF" it is a large enough amount of gasoline poured on a young, small, sick, delicate or sensitive tree. A large, older tree and a small amount of gas is not a problem. It depends on all those factors if it would harm or kill a tree. There is potential.
Ounces
No you would measure it in kilos, because its mass and volume are too great to measure in liters alone.
A spirometer is used to measure the amount of air in our lungs.
gallons
Litre
A balance is a very sensative set of scales. You would use it to measure a very tiny amount of mass.
pH is a measure of the acidity. concentration of salts would be molarity.