One of these is Milton Resnick  

#5

That is CORRECT!
How did you come to that conclusion may I ask?
Google search? Years of study? Process of Elimination of the other 5?

Art school, decades of work for art museums, particular interest in Abstract Expressionism, and dumb luck.
Oh, and I have a good eye and enjoy a bit of a challenge.
Oddly, that pretty much sums up how I ended up marrying so well, too!

great comment...

I honestly can't see much difference and couldn't pick the correct one if my life depended on it.
Feel like trying to explain it to me?:)

Okay. To be completely honest, I first did a basic goggle image search to quickly re-familiarize myself with Resnick's work and looked over the top fifty or so thumbnails for about two minutes. Then I went back and immediately discounted your first three images because they either appeared as works on paper (for which I have almost no personal reference) or because it seemed that the artist(s) was/were employing chiaroscuro techniques to model forms in 3-dimensional space. The fourth shows recognizable rendering of foliage. That left the last two images. #5 looked like an oil painting to me and the large deep-black elements in #6 just didn't feel right. Hence my guess.
All of my other BS above still applies, though!

Makes sense, thanks. Time for me to google chiaroscuro:)