"needs to make exactly k nano liters of the oxide in any of the test tubes"

When you have k nano liters in a test tube that is not #1 the checker gives WA. My AC program was getting WA because my final test tube wasn't #1...

Got WA #1 with the following output:
4
2 5
4 3
3 5
5 1

It seems correct, except for the fact the final tube is number 5, and not #1.
Anyways, nice problem <3