Which statement correctly defines the selectivity factor alpha and its effect on resolution Rs?

Which statement correctly defines the selectivity factor alpha and its effect on resolution Rs?

• A. Alpha = k'_2 / k'_1, and increasing alpha increases Rs up to practical limits.
• B. Alpha = k'_1 / k'_2, and increasing alpha reduces Rs.
• C. Alpha is the sum of the two k' values.
• D. Alpha is the square root of the number of theoretical plates.

Answer: (A)