How can i find the number of electrons are gained or lost

15. 1 were lost

16. 3 were gained

17. 2 were lost

18. 1 was gained

You can figure that out by looking at the number nest to the molecule with a  plus or minus sign next to it

+ = gained

- = lost

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.

air

in a tire you fill a tire with air

then a couple days later you check the air pressure in the tire

hope this mark me brainliest