What are extensive properties?

For which of the following reactions,$\Delta H$ is equal to $\Delta U$ ?

Predict the change in internal energy for an isolated system at constant volume.

During the isothermal expansion of an ideal gas,its enthalpy change is ......

Extensive properties depend on the quantity of matter,while intensive properties do not. Classify the following properties as extensive or intensive:
Mass,internal energy,pressure,heat capacity,molar heat capacity,density,mole fraction,specific heat,temperature,and molarity.

According to thermodynamics,when can a process be called reversible?