Question

Aqueas solution of Ammonia is used to remove grease stain from clothes .why?

Answer 1

That said, ammonia is an alkaly. As such it will saponify oil and grease. The resulting soapy substances will be removed by water. Of course this a simplistic explanation, because there are many different possible interactions between ammonia and lipids, depending on the kind of lipids, temperature, concentration, etc..

Answer 2

Because it's an alkaline solution