Flash of lightning reaches earlier than the sound of thunder. Why?

Explain why there is usually a time delay between observing a flash and hearing a thunder?

$(i)$ How do bats make use of ultrasonic waves to catch their prey? Explain.
$(ii)$ $A$ radar signal is reflected by an aeroplane and is received $2 \times 10^{-5} \text{ s}$ after it was sent. If the speed of these waves is $3 \times 10^{8} \text{ m s}^{-1}$,how far is the aeroplane?

What change,if any,would you expect in the characteristics of musical sound when we increase $(i)$ its frequency and (ii) its amplitude?

$A$ source is producing $1500$ sound waves in $3$ seconds. If the distance covered by a compression and an adjacent rarefaction is $68 \, cm$,find $(a)$ frequency,$(b)$ wavelength,and $(c)$ velocity of the sound wave.

Give reasons for the following:
$(a)$ The reverberation time of a hall used for speeches should be very short.
$(b)$ $A$ vibrating body produces sound. However,no sound is heard when a simple pendulum oscillates in air.
$(c)$ Sounds of same loudness and pitch but produced by different musical instruments like a violin and flute are distinguishable.