Which one of the following is the natural phenomenon based on a simple periscope works?

Which one of the following frequency range is sensitive to human ears?

Which of the following statement(s) about a fluid at rest in a cup is/are correct ?

1. Pressure is same at all the points in the fluid.

2. Pressure is exerted on the walls.

3. Pressure exists everywhere in the fluid.

Which one of the following device is used to measure atmospheric pressure?