An organic acid containing carbon, oxygen and hydrogen only has molar mass of 132 g. 6.6g of this acid require 80mL of 1.25M NaOH for complete neutralization. How many carboxylic groups are present in one molecule of this acid?

Let us consider organic acid as ‘A’.
Moles of A = mass of A/Molar mass = 6.6/132 = 0.05
Molarity of NaOH = 1.25M
And volume of NaOH  = 80 mL
Therefore, moles of NaOH = molarity × Volume
= 1.25×80×10^-3 = 0.1 moles.
SO, 0.05 moles of A requires 0.1 moles of NaOH
1 mole of acid requires x moles of NaOH
x = 0.1/0.05×1 = 2
So for neutralisation of 1 mole of A, we need 2 moles of NaOH. Therefore given acid is dibasic and contains 2 -COOH groups.