b. What are the dew point ranges?...

Actually thinking about this, I would say that the range for the dew
point is that the dew point cannot fall below the air temp and it
cannot be higher then the air temp.

The dew point can never be greater than the air temperature but can most
certainly be below the air temperature. My temp right now is 15.1C and
the dew point is 12.9 degrees C. Quite normal.

Yes you are right, I must not have had enough coffee or something to
have posted that.
Yes the dewpoint is always lower then the air temp since the dew
point can't go above the air temp.
So there is no range that I know of to the low end of the dew point,
the colder it gets the lower the dew point will get unless humidity is
100% and then the air temp and the dew point will be the same.

Craig