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You can put one maybe 2 one-inch fishes in your one gallon aquarium
You should only have 1 fish per gallon of water in a fish tank. I wouldn't put more than 2 or 3 Neon Tetras in a 4 gallon aquarium with 1 Betta.
Most Aquarist use this rule of thumb to put fish in an aquarium, 5 inches of adult fish for every gallon of water in the tank. The five inches only takes in the head and body. Do not use the tail in the measurement.
Get a small Aquarium Fish Net, get the body of the Fish, put it in the toilet.
Depends on the kind and size of the fish. You should also take in to consideration how large they will get at adulthood. A good rule of thumb to go by is 1 gallon of water for every 1 inch of fish. So for example: 3 2" fish should be in at least 6 gallons of water. To be safe I would put them in a 10 gallon aquarium.
Depends on whether or not you have aeration (an air pump). If no aeration, then you shouldn't put more than 2-3 fish "inches" (total inches of fish) in the aquarium. If you do have aeration going, then you can double this amount and have up to 6 inches of fish.
Good choices would be a pea puffer, spotted puffer, or a figure 8 puffer
You can put 3 mice in a 10 gallon tank. It is best to not put 4 mice because the ventilation will not be enough and will smell horrible and possibly cause distress to the mice.
you can put a betta in a 5 gallon tank
precisely 2.2
you can as long as you have a filter and a fish tank
The fish will be living alone in the aquarium. And that's ok.