Again great job! They all look correct except 20. is 3.7 due to sig fig of least precision, which you have a mark by!! You don't even need help!;) Here comes the next chemical engineer! :)
Answer:
last one is the correct and most suitable option.
Hope it helps!!!
The answer is D. obsidian. Or at least I think it is. Just guessing based off me playing Minecraft 6 years ago haha