If RR plants are crossed with rr plants, would the offspring have round or wrinkled peas? Why?

It depends. If the round peas are the dominant trait, it would be the answer. Vice versa. The dominant trait will be the answer.
Why? Because if you cross RR ( both dominant ) with rr (both recessive), 75% of the time it would turn out to be dominant. (Think of punnet squares)

The atmosphere is full of water

Evaporation and transpiration change liquid water into vapor, which ascends into the atmosphere due to rising air currents. ... Clouds are, of course, the most visible manifestation of atmospheric water, but even clear air contains water — water in particles that are too small to be seen.