An automobile achieves a gas mileage of 24.5 mi/gal. How many kilometers can it travel on 1.5 L of gasoline?

They are all decomposition reactions.

Idon't know hope someone you

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

So the main goal for the elements is stability which is a complete/full valence shell and typically the magic number for a stable element is 8 valence electron but not always. so elements to the left of the periodic table tend to be way less stable then those on the right, so the elements on the left are much more reactive.