紙與碎紙的重量

2) > X (kg)

如果將該疊紙張經碎紙機碎成紙條後,紙條的總表面積變大,空氣浮力把紙條向上推,紙條重量降低,但真空環境下,紙條跟疊紙 重量為 1) = X (kg)

the answer is 2
after slicing the paper into pieces, it will trap more air inside the pieces of paper, which increases the mass of the paper

p.s. but when we just consider the isolated mass of the paper, the answer is 1

要不要考慮buoyance?

From the physics point of view, if every bits of paper have been collected after stripping, the mass of stripped paper is the same as before, i.e. X kg.

This is the Law of Conservation of Mass.