Which of the following is the expression for longitudinal diffusion in the column, if ‘γ’ represents obstruction factor, ‘dM’ represents particle diameter, ‘DM’ represents Solute diffusion co-efficient and ‘λ’ represents function for packing uniformity?

• A. λ dM
• B. 2 γ DM
• C. DM γ
• D. λ/dM