Which one of the following is not a state function?

Which of the following is correct regarding the internal energy of a substance?

Fill in the blanks:
$(i)$ $A$ system that allows the exchange of energy but not matter with the surroundings is called a ........ .
$(ii)$ The total amount of energy consisting of the internal energy of a substance plus the product of its pressure and volume is called ........ .
$(iii)$ The change in energy that occurs when a chemical reaction is carried out at constant pressure is called ........ .

For a massless piston undergoing an expansion of $\Delta V$ at constant temperature against a variable external pressure $P$,which equation represents the work done?

For the isothermal reversible expansion of an ideal gas,which of the following is correct?

Given below are two statements $ : $
Statement $I :$ When a system containing ice in equilibrium with water $(\text{liquid})$ is heated, heat is absorbed by the system and there is no change in the temperature of the system until whole ice gets melted.
Statement $II :$ At the melting point of ice, there is absorption of heat in order to overcome intermolecular forces of attraction within the molecules of water in ice, and the kinetic energy of molecules is not increased at the melting point.
In the light of the above statements, choose the correct answer from the options given below $ : $