A hot liquid X was allowed to cooled in air. The temp. was measured every 5 sec. Y axis shows temp. in deg. C of 10 deg. intervals & X axis...

The pattern of the process as described above is that the
temperature of a substance originally in liquid form and above the room temperature when
allowed placed in open air, drops to a lower temperature and stays there for some time.
Again the temperature falls and after some time stabilizes at that temperature for a
very long period.

This pattern of temperature indicates to
the possibility that when the temperature stopped falling for some time, the liquid was
loosing latent heat of fusion. Due to this though heat was being removed from the
substance its temperature did not change. Instead the loss of heat resulted in
solidification of the liquid. Thus this intermediate stable temperature is the melting
point of the liquid.

The final stable temperature is
because the solidified substance has reached room temperature. After this, in absence of
temperature difference between the substance and the surrounding air, there is no
further energy loss.

Based on the above logic, answer to
the question are:

Melting point of substance X = 50 degrees
C.

Room temperature = 33 degrees
C.

Energy is being lost continuously from start of the
graph till temperature reaches 33 degrees C. Once this temperature is reached there is
no further energy loss.