Assertion (A) : Two persons on the surface of moon can not talk to each other.

Reason (R) : The speed of sound decreases with the decrease in temperature.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : The speed of ultrasound waves is higher than supersonic waves.

Reason (R) : Supersonic is used for objects travelling with speed greater than speed of sound in air.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

What is the audible range of frequency for humans?

For which range of frequencies are the human ears most sensitive?