I believe it is the second option
I think the answer for #3 is A not 100% sure but hope I can help!
This is a really hard question. Because if you change it to 1,000 then that's only one. If you add the decimal so it's 1,000. , then that's 4 if you change it to 1,040, that's 3. So you can not change that to 2 significant digits.
There is 9.375 g of nitrogen. This is because when a half-life passes, the mass becomes 2 times less. Since two half-lives have passed, you need to divide by 4.
