Questions

I am black gold i.e charcoal. It is black when it is not used and when using it is red due to fire and when used it is in grey color as it becomes ash. 

Sublimation is a process when a solid changes directly into gas instead changing into liquid first. Dry ice is an example of Sublimation process because it doesn't change into liquid CO2 and directly change into gaseous CO2 when heated.

Hence, Dry ice is an example of Sublimation process. 

The size of gear is usually specified by pitch circle diameter.

Can’t delete a row from primary table if there are related rows in secondary table.