Which of the following leads to a higher rate of diffusion?

a. cooled gas
b. higher molar mass of particles
c. higher velocity of particles
d. reduced temperature

I thought the answer is d

D. Reduced temperature

> b takes place in the gas phase in an isothermal tubular reactor. the feed is one mole of a per one mole of c, an inert. the entering temperature and pressure are 427°c and 10 atm, respectively. the gas constant r = 0.08206 atm · l/mol · k.