Answer: The molar mass of monoprotic acid is 87.72 g/mol
Step-by-step explanation:
To calculate the concentration of acid, we use the equation given by neutralization reaction:

where,
are the n-factor, molarity and volume of monoprotic acid
are the n-factor, molarity and volume of base which is NaOH.
We are given:

Putting values in above equation, we get:

To calculate the molecular mass of acid, we use the equation used to calculate the molarity of solution:

We are given:
Molarity of solution = 0.0456 M
Given mass of acid = 0.140 g
Volume of solution = 35.0 mL
Putting values in above equation, we get:

Hence, the molar mass of monoprotic acid is 87.72 g/mol