These questions are way too basic- the first 4 can be answered directly from the definition of each term, and there is no thinking involved. The 5th question can be answered with knowledge from 1 lesson in graph theory.
Questions 3 and 4 I simply don't have the background (I've never heard of a B-tree, and I've heard of heap sort but I don't know the algorithm).
Question 5 I'd not seen before, but an algorithm was quite obvious because I've taken a course on graph theory (of course, my answer could easily be wrong).
My tentative position is that these questions are easy if you've covered the relevant material before, and very hard to impossible if not.
Disclaimer 1: my degree was mathematics, not computer science, and I don't work as a software developer (though I do write code every day).
Disclaimer 2: one of the questions I "knew" the answer to, I got wrong!
There's a lot of people who are very confidently giving wrong answers to questions, which weighs against that position.
Given the selection bias we would expect among respondents, have you thought about how you will interpret the responses?