<u>Answer:</u> The mass of original oxalic acid sample is 6.75 grams
<u>Explanation:</u>
To calculate the concentration of acid, we use the equation given by neutralization reaction:

where,
are the n-factor, molarity and volume of acid which is 
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 mass of solute, we use the equation used to calculate the molarity of solution:

Given mass of oxalic acid = ? g
Molar mass of oxalic acid = 90 g/mol
Molarity of solution = 0.075 M
Volume of solution = 1.00 L
Putting values in above equation, we get:

Hence, the mass of original oxalic acid sample is 6.75 grams