no
No, tetras of the same type tend to school together, although some tetras are know to be a bit more aggressive than others.
No, Neon Tetras and Goldfish do not belong in the same tank. Goldfish prefer cold water, while Tetras are more of a tropical fish.
Tetras lay eggs. only you lay eggs if you are a girl!
A fish's colours fade when it is depressed and/or lonely. When it is back with a small school of the same breed, its colours reappear and it will be more active. Also, some tropical fish food has colour enhancing ingredients that make the fish's scales more glossy and bright.
Swimmers' trunks if there are more swimmers. Swimmer's trunks if there's only one swimmer. The problem is that trunks is plural regardless of the number of the previous noun in the compound and so, from the context of this question, it cannot be distinguished whether there's one or more swimmers. Had it been "the swimmers' caps" it would be possible to derive that there are more swimmers. Alternately it would be "the swimmer's cap".
Plug it in!!
The best thing you can do to make your Oscar more active is to raise the temperature of the heater you have.
Many inexperienced swimmers misjudge their ability. That causes them to try more than they are capable of.
That is fine. You might consider getting some corydoras catfish.
Leopard geckos are nocturnal and are probably much more active as you are sleeping. There is nothing to worry about.
Several things can be done; remove the fish to another tank, remove the fish that are harrasing the tetra, or get more tetras. Getting more tetras should resolve the problem as there will be more than one target.
Might be time to get a tank divider to separate them. Although, typically, mollies don't eat tetras usually unless they are fry.