It is probably gas as pure water starts boiling at 100d degrees C
Water vapour and a drop in temperature to condense water vapour into a cloud. Something to see the cloud also, such as "pollution" particles.
C because they are both going in a constant speed
rest is the state of a body which is stationary relative to a particular frame of reference or another object. When the state of a body does not changes with time with respect to its surroundings in a particular frame of reference that time it is said to be at rest.
in other words we can say that when a body has zero velocity and its position is not changing with time relative to its surrounding then it is said to be at rest.
For example a chair on which you are sitting is at rest or a table on which your desktop is kept is rest because its position is not changing.