A solid substance is at $30°C$. To this substance heat energy is supplied at a constant rate. Then temperature versus time graph is as shown in the figure. The substance is in liquid state for the portion (of the graph)

Liquid oxygen at $50\  K$ is heated to $300\  K$ at constant pressure of $1\  atm$. The rate of heating is constant which of the following graphs represents the variation of temperature with time

On a hot day, placing a cup full of ice water on the table heats up as cup of hot tea on the same table cools down. write the reason.

A substance is cooled at a constant power. Its temperature vs time graph is shown. The value of $S_{solid} : S_{liquid} : S_{gas}$

A copper block of mass $2.5\; kg$ is heated in a furnace to a temperature of $500\,^{\circ} C$ and then placed on a large ice block. What is the maximum amount of ice (in $kg$) that can melt? (Specific heat of copper $=0.39\; J g ^{-1} K ^{-1}$ ;heat of fusion of water $=335\; J g ^{-1})$

What is called change of state of matter ?