An acid-base titration is a technique where a solution of known concentration of acid/base is used to determine the concentration of an unknown solution of acid/base. These titrations typically use a pH indicator solution to denote the end point of the reaction. A pH indicator is a compound added in small quantities toa solution to indicate the pH visually(generally by appearance/disappearanceor change in colour). A typical procedureis as follows: A certain volume ‘V1’ of unknown concentration ‘M1’ of HCl istaken in a conical flask, to which a few drops of phenolphthalein indicatorsolution is added. The solution remainscolourless. From a burette (a graduateddropper) a solution of NaOH, whoseconcentration is known, ‘M2’, is addeddropwise into the conical flask until a palepink colour is obtained and is termed as the end point. The amount of solution dispensedfrom the burette to obtain the end point is noted as ‘V2’. Phenolphthalein indicator change sits colour to pink only when the pH of the solution is above 9.5. Similarly, another indicator,methyl orange, is red in colour below pH 3.7 and yellow above. Given below is a graph of pHof the solution in the conical flask and the reading of the burette in the course of the titration. The equivalent point is theoretically defined as the point in the graph where the number of moles HCl in the conical flask becomes equal to the number of moles of NaOH run down the burette. Note the difference between end point and equivalence point.

Which is the correct graph that represents the titration of NH4OH (from burette) with HCl?