Answer:
It will decrease by 2 units.
Step-by-step explanation:
The Henderson-Hasselbalch equation for a buffer is
pH = pKa + log(base/acid)
Let's assume your acid has pKa = 5.
(a) If the base: acid ratio is 1:1,
pH(1) = 5 + log(1/1) = 5 + log(1) = 5 + 0 = 5
(b) If the base: acid ratio is 1:100,
pH(2) = 5 + log(1/100) = 5 + log(0.01) = 5 - 2 = 3
(c) Difference
ΔpH = pH(2) - pH(1) = 5 - 3 = -2
If you increase the acid:base ratio to 100:1, the pH will decrease by two units.