If it is a recruiter from the company doing the hiring, they want to pay you as little as possible. Do not give a number first. If forced, say "any reasonable market salary". If they still push, give a wide range like "somewhere in the $100k to $300k range" (assuming your goal is $200k)
It's a game with exactly one rule: whoever puts a number out first loses.
There've been several times in my career -- especially when starting out -- where I just plain underestimated what they were willing to pay me. Once I just bit my tongue and stopped myself from saying "But of course, I wouldn't expect you to pay me THAT much..." And the next thing they said was "We could pay you that."
My first job out of college, they asked me "What's the least amount of money you'd work for." And when I stressed it was a very low number, that it was the barest minimum that I could ever consider -- that was what they offered me.
Don't learn this the hard way. They'll act all conversational and wait for you to say something. (If the silence gets awkward, you're free to say something like "How much are you offering for this position?") It wouldn't hurt to rehearse a few lines to turn the question back to them, so you're ready when this comes up.