The correct option is D Inertial Collector
Inertial collectors works on the principle that inertia of Suspended Particulate Matter in a gas is higher than its solvent and as inertia is a function of the mass of the particulate matter this device collects heavier particles more efficiently. A Cyclone is a common inertial collector used in gas cleaning plants.
Gravity separation is an industrial method of separating two components, either a suspension or dry granular mixture where separating the components with gravity is sufficiently practical and works on the principle of inertia. However, they are not used in control of industrial pollution.