Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?

Take two concal flasks and paint one white and other black.Fill both with water. Place the conical flasks in direct sunlight for half an hour to one hour. Touch the conical flasks . Which one is hotter ? You could also measure the temperature of the water in the two conical flasks with a thermometer. Can you think of ways in which this finding could be used in your daily life ?

Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?