Learn English – Did you go (somewhere/anywhere) exciting at the weekend

Any of those sentences could be used and seem completely natural in different contexts. You choose each among those expressions based on what you want to communicate.

Are you talking about one chair or many chairs? That (obviously) determines whether you choose the plural or not. If I asked about multiple spoons, but you answered me with a singular response, it would seem odd. For example, if I said "Would you get me two spoons from the drawer please?" and you responded "There's no spoon here." If I ask about a singular and you responded with a plural it wouldn't be as odd. If I say "Go tell Joe he has a phone call." you could say "There are no Joes in this room - I don't know who you're talking about." even though it's more likely you would say "Joe isn't here."

Are you talking about one specific chair or just any chair? That determines whether you say "there is no chair" or "there isn't a chair". This can be tricky because it really depends on what is in your mind when you say it, and not necessarily anything that has been said earlier. I could say "When you get there, sit in the chair." and if there are only couches when you get there, you might tell me "There is no chair here." (the specific chair that you were going to sit in isn't there) or "There aren't any chairs here" (you looked for any chair to sit in and there were none available).

In the movie the Matrix, there is a scene where a boy is bending a spoon with his mind and he says that to do that first you must realize there is no spoon. He is speaking about a specific spoon. If I asked you to get me a spoon from a drawer that had no spoons in it, you could say "there isn't a spoon in here (for me to give you)." or "There aren't any spoons in here, just forks." or "There's no spoon in here (the specific spoon you want isn't here)." All of those statements are fine and sound natural.

You thought they were size nine (US) at the time you ordered them (in the past). You now (in the present) know they are size nine (UK).

I thought they were US size nine but now I know they are UK size nine.

When I met my husband I thought he was a nice guy but now I know he's a total jerk.

Previous assumption, present knowledge.