A titration measures a concentration you cannot see by reacting it away against one you can. A pipetted aliquot of the unknown acid waits in the flask; standard base drips from the burette until the indicator turns. At the equivalence point the moles have exactly annihilated, and $C_a V_a = n\,C_b V_b$ — read aloud: C-a V-a equals n C-b V-b. Every symbol: $C_a$ is the analyte's concentration in mol/L (the unknown), $V_a$ the aliquot volume, $C_b$ the titrant's concentration off the bottle, $V_b$ the titre the burette delivered, and $n$ the mole ratio — moles of ANALYTE per mole of titrant, a pure number. Subscript a is the flask, subscript b is the burette; that convention never changes.

The mole ratio is where marks are lost. HCl against NaOH is one-to-one, so $n = 1$. Sulfuric acid carries two protons, so one mole of acid spends two of base and $n = 0.5$ — acid per base, and the fraction feels backwards until you say the sentence out loud. One more discipline: because $V_a$ and $V_b$ meet as a ratio, millilitres cancel and nobody converts. The instant a question asks for moles, that immunity ends — mol/L only cancels against litres, and the ÷1000 becomes compulsory.