We can hear sound of frequency:

1. 10 Hz
2. 500 Hz
3. 100,000 Hz
4. 50,000 Hz

Sound cannot travel in:

1. gases
2. liquids
3. solids
4. vacuum

The minimum distance required between the source and the reflector so as to hear the echo in air is:

1. 10 m
2. 17 m
3. 34 m
4. 50 m

Wavelength is measured in:

1. kg
2. second
3. litre
4. metre