Aitken particles are

Answer: Option D

Aitken particles are activated in humid air, cloud's condensed nuclei and Hygroscopic particles.
Aitken particles have been defined as those airborne particles having radii less than 0.1 m but larger than those of molecules and small ions.
Those with a particle size between 5.0 × 10^-3 and 0.2 μm are called Aitken nuclei, those with a particle size from 0.2 to 1 μm are called large particles, and those with a particle size greater than 1 μm are called giant particles.