Why is an alkali metal like sodium so reactive?

The valence electrons determine how reactive an element is, and since Sodium and other alkali metals could easily lose an electron, they become very reactive to be stable. 

If the water vapor content stays the same and the temperature drops, then the relative humidity increases. its vise versa.if the water vapor content stats the same and the temperature rises, the relative humidity decreases. so, yes, i'd say that temperature and humidity have a strong relationship.