When ethyl iodide is treated with alcoholic caustic potash , we get
When ethyl iodide is reacted with alcoholic potash we get ethylene. This reaction is called as dehydro halogenation which is a elimination reaction. This is a process of preparing alkenes from haloalkanes.
CH3−CH2−I+alcKOH→CH2=CH2+KI+H2O.
Hence option C is correct.