ANS:D - none of these.

The correct statement is: none of these. Diffusivity decreases with increase in temperature:

1. • This statement is generally incorrect. In most cases, diffusivity tends to increase with an increase in temperature. This is because higher temperatures typically lead to greater kinetic energy of molecules, resulting in more rapid movement and increased diffusion rates. As a result, the diffusion coefficient (a measure of diffusivity) often increases with temperature, following Arrhenius-like behavior.
2. Diffusivity increases with increase in molecular weight:
   • This statement is generally incorrect. In most cases, diffusivity tends to decrease with an increase in molecular weight. Heavier molecules generally have slower diffusion rates compared to lighter molecules due to their larger size and increased resistance to movement through a medium. As a result, the diffusion coefficient typically decreases as molecular weight increases.
3. Diffusivity increases with the size of the individual molecule:
   • This statement is generally correct. Larger molecules often have slower diffusion rates compared to smaller molecules due to their larger size and increased resistance to movement through a medium. As a result, the diffusion coefficient tends to decrease with increasing molecular size. However, it's important to note that molecular size is not the only factor influencing diffusivity, as other factors such as molecular shape, polarity, and interactions with the surrounding medium also play roles in determining diffusion rates.