I have a question about chains. Can you use a 10 speed chain on 7 speed cog set? And the reverse, can you use a 7 speed chain on a 10 speed cog set? Any and all response is welcome.

I think I should be more clear about my question. Can I use a 7 speed chain with a 10 speed chainring. Please disregard the first post.

No.

To explain a bit, 6,7,8 speed use the same chain. 9,10, 11 each use their own chain. Cynically speaking, this is because bike manufacturers figured out that the more quickly they can make bikes and parts obsolete, the more crap they can sell.

A 7-speed chain will run fine on ONE 10-speed ring. Spacing between rollers remain the same. Might not be so happy on a double/triple. Haven’t tried. Will not be happy at all on a 10-speed cassette. May also object to being run through a more speeds derailer.

You should be fine.
As stated a 10S Cassette won't like it but a chain ring should be fine. You'll probably be fine on a double too. Going the other direction 7 speed cranks don't like 10s chains as it can drop between the wider 7 s chain ring spacing.
Narrower 10s Derailleurs also don't often like 6-7-8 chains.