What state must water be in to be invisible in the sky?

Answer

Gaseous state (water vapor)

Water in its gaseous state, known as water vapor, is invisible. It only becomes visible once it cools enough to condense into liquid droplets or solid crystals.

What state must water be in to be invisible in the sky?

#Videos

NASA Spotlite: What are clouds made of? - YouTube

waterairgascloudvapor