A student takes some water in a beaker and heats it over a flame for determining its boiling point. He keeps on taking its temperature readings. He would observe that the temperature of water:

(1) keeps on increasing regularly

(2) keeps on increasing irregularly

(3) first increases slowly, then decreases rapidly and eventually becomes constant

(4) first increases gradually and then becomes constant

The correct option is D. During any phase transition i.e.  melting, boiling, freezing, etc the temperature of the system remain constant until all the substance changed into the other state. 
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