emptriv has about 20,000 questions, many on those categories, and of varying degrees of difficulty. I'll attach the data file for the "Science" category, for example. The format is tab-separated values (suitable for importing into Excel), and the fields are:
"CATEGORY" "Question" "Difficulty" "Answer #1" "Answer #2" "Answer #3" "Answer #4" "Answer #5" "Number of Correct Answer"
For instance, here's a sample question:
"SCI" "What is the study of soils known as?" "86" "Geology" "Pedology" "Petrology" "Terraology" "Frenology" "2"
Difficulty is a number from 1 to 100. There are not necessarily 5 possible choices for answers of all questions, but there are usually at least 4.
I have all 20,000 emptriv questions in a big fat Excel spreadsheet (6mb) if you're really interested, but the questions in the attached file should help fill out your science category. Want more, let me know.