Answer:
The answer is 2.2
Step-by-step explanation:
Since the above substance is a weak acid it's pH can be found by using the formula

where
Ka is the acid dissociation constant
c is the concentration of the acid
From the question
Ka = 4.0 × 10-⁴
c = 0.1 M
So we have

We have the final answer as
2.2
Hope this helps you