The dew point is a measure of the amount of moisture in the air; it represents the temperature at which air becomes saturated with moisture and can no longer hold all of it in the form of vapor.
If the temperature increases from 90°F to 100°F, the dew point will remain at 50°F, provided that the amount of moisture in the air does not change.
So, the correct answer is: The dew point still remains at 50°F.