Consider the following table.

Animal	Frequency range of sound waves
Elephant	$15-12000 \mathrm{Hz}$
Human	$20-22000 \mathrm{Hz}$
Dog	$65-45000 \mathrm{Hz}$
Chicken	$125-2000 \mathrm{Hz}$

A cat made a purring sound that had a frequency of $35 \mathrm{Hz}$. Which of the animals mentioned in the table can hear the purring?

Aditi hangs four steel dishes of the same size but different thickness.
She hits each of them with an iron rod.

The thicker the dish, the lower will be the vibration. Which dish will produce the loudest sound when hit?

An astronaut is moving in space when a big explosion occurs about a hundred meters behind him. How will the astronaut come to know about the explosion?