The property of viscosity in gas is due to

The origin of viscosity of a fluid is the combined effect of inter molecular force of attraction (cohesive force) and transfer of momentum of molecules in a direction normal to the direction of flow due to collision between the molecules. In case of gaseous substance, intermolecular separation is large, so cohesive force is less, so chief reason of viscosity in gassesous substance is collision between the molecules. so option (2) is correct.