Answered

Why does the heat of the heating element stop when the desired temperature in an electric iron is reached?

Athe thermostat blade opens electrical contacts.
Bthe circuit through the element is closed.
Cthe switch bypasses the thermostat.
Dthe contacts on the blade touch.

Verified Answer :

Erudite1

The heat stops because the thermostat blade open the electrical contacts and current is cut off.

Greenleafable

The heat of the heating element stops when the desired temperature in an electric iron is reached because A. the thermostat blade opens electrical contacts. 
This is why heating ceases to rise or fall (it stops completely) once the thermostat's blade opens.