Which of the following phenomena can be demonstrated by light,but not with sound waves in an air column?

When an unpolarized light of intensity $I_0$ is incident on a polarizing sheet,the intensity of light which does not get transmitted is

Two polaroids are kept crossed to each other. Now one of them is rotated through an angle $45^{\circ}$. The percentage of incident light now transmitted through the system is ......$\%$

Two polaroid sheets are placed one over the other with their axes inclined to each other at $30^{\circ}$. The ratio of the intensity of the unpolarised incident light and the polarised emergent light is

The angle between the polarizer and the analyzer is $45^o$. The percentage of polarized light passing through the analyzer is........$\%$

Two linear polarisers are placed coaxially. The transmission axis of the first polariser is at $30^{\circ}$ from the vertical,while the second one is at $60^{\circ}$ from the vertical,both in the clockwise sense. If an unpolarised beam of light of intensity $I_{0}=20 \,W/m^{2}$ is incident on this pair of polarisers,then the intensities $I_{1}$ and $I_{2}$ transmitted by the first and second polarisers respectively,will be close to: