Pls provide the solution.

Dear Student,
(b)
(i) We know that the slope of the temperature-time graph is inversely proportional to the specific heat capacity. And specific heat capacity in the liquid state is greater than specific heat capacity in the solid-state, which means that the slope of the solid-state is greater than the slope of the liquid state. Therefore the slope of CD is less than the slope of AB.

(ii) Boiling point of the substance is $t_2°C$
     And melting point of the substance is  $t_1°C$.
Regards