Question

b. Astronauts on the moon can not hear each
other directly​

Answer 1

Because there is no atmosphere at moon. Sounds needs a medium to travel. ... Due to absence of air on moon, sound cannot travel so astronauts cannot hear each other.

Hope! This will help you ✅✅

Answer 2

$\bold{Answer\;:-}$

• Sound needs medium for propagation. As there is no medium in the atmosphere, propagation is not possible, that is why astronauts on the moon can not hear each other directly.

$\bold{Hope\;it \; helps\;!}$