Explain;

when ammonium nitrate is dissolved in water contained in a beaker,it becomes cold

When ammonium nitrate is dissolved in a beaker containing water, the beaker becomes cold because it is an endothermic reaction that is it absorbs energy from the surroundings in the form of heat. Thus hydrating ammonium nitrate is an endothermic reaction, because of which the beaker becomes cold. 

@ Radhika, very good answer. Keep it up :)