Question

Active mass of 2 moles of NaCl is kept in 4 ltr vessel at NTP is

Answer 1

The active mass of solids and pure liquids is a constant quantity (unity) because it is an intensive property i.e. number of molecules present per unit volume do not change because density and molecular weight of solids and pure liquids are constant. But it doesn't apply for gaseous substances because for them no. of gaseous molecules present per unit volume change with change in volume of vessel.

Since, Nacl is a solid. That is why active mass of solid i. e. Nacl is 1.