Which of the following statements is $NOT$ true?

$A$ train, standing in a station-yard, blows a whistle of frequency $400\,Hz$ in still air. The wind starts blowing in the direction from the yard to the station with a speed of $10\,ms^{-1}$. What will be the frequency and speed of sound for an observer? (The speed of sound in still air is $340\,ms^{-1}$)

If the velocity of sound in a gas is $360\, m/s$ and the distance between a compression and the nearest rarefaction is $1\, m$,then the frequency of sound is ..... $Hz$.

Sound waves travel at $350 \ m/s$ through warm air and at $3500 \ m/s$ through brass. The wavelength of a $700 \ Hz$ acoustic wave as it enters brass from warm air:

Mention the type of ultrasonic waves and their frequency.

$A$ narrow sound pulse (for example,a short pip by a whistle) is sent across a medium.
$(a)$ Does the pulse have a definite $(i)$ frequency,$(ii)$ wavelength,$(iii)$ speed of propagation?
$(b)$ If the pulse rate is $1$ after every $20 \; s$,(that is,the whistle is blown for a split of a second after every $20 \; s$),is the frequency of the note produced by the whistle equal to $1/20$ or $0.05 \; Hz$?