Question

Is it not that if number of molecules in a substance or system increase it will exert more pressure on the wall of container so pressure must be extensive in nature. However pressure is said to posses intensive property. Why?

Answer 1

Presseure is intensive property only if we are keeping the volume of gas as flexible(changing). In according to ideal gas equation
PV=nRT of P=nRT/V
If we remove certain number of moles from the container that means the volume of container is also reduced proportionally. So the number of moles per unit surface area will be same. Hence the pressure of container will not change due to change in number of moles.
But alternatively if we keep the volume constant, then definitely pressure in extensive property. Because increasing the number of moles will increase the pressure inside.