Button that doesn't appear until all remaining buttons are pushed?

I'm not a fan of having that many variables, and generally just use a "Counter" var instead, and increment it each time a question is opened, and then at the end just check against what I know to be the number of questions (if counter = 25 in your case)

It is rather hard coded, vs the "if ALL" option presented above, but if you know you're only going to ever have that set number of questions it's a lot easier to juggle 1 variable IMO. You'll still obviously need the triggers on each question, but you'd need that either way.