In this lab you will be given two polaroid sheets with unlabeled transmission axes. how can you tell, when looking through both polaroid sheets at the same time, if the transmission axes are crossed?
1. if the transmission axes are crossed, you will see one bright line when you look through the polaroid sheets.
2. if the transmission axes are crossed, it will be very dark when you look through the polaroid sheets.
3. if the transmission axes are crossed, it will be bright when you look through the polaroid sheets.
4. if the transmission axes are crossed, you will see a bright "+" shape when you look through the polaroid sheets.

2. If the transmission axes are crossed, it will be very dark when you look through the polaroid sheets

Explanation:

Polaroids sheets produces linearly polarized light from an un polarized light. Now,  when two polaroids are kept in such a way that their transmission axes are crossed ( that is 90° to each other). No light would pass to the other end, because their transmission orientation are different.

Thus, the correct answer to the question will be

2. If the transmission axes are crossed, it will be very dark when you look through the polaroid sheets

and rest all options are wrong because they all talk about some kind of brightness.

d is the correct answer