Fetch't, let me see't.....Fetch me the Handkerchief-my mind misgives...The handerchief! (III.iv.82-88)
I say,it is not lost...Why,so I can,sir,but i will not now. This is a trick to put me from my suit .pray you, let Cassio be received again...Come,Come You'll never meet a more sufficient man(III.iv.82-88)
(Striking her) Devil! (IV.i.232)
I have not deserved this. (IV.i.233)
My lord, no one will believe this in Venice, even though I’d swear I saw it with my own eyes. That was too much. You should apologize. She’s crying. (IV.i.234-236)
Maybe because I’m black, and I don’t have nice manners like courtiers do, or because I’m getting old—but that’s not much—She’s gone, and I’ve been cheated on.(III.iii.267-272)
This scene is one of the scenes that display one of Othello's external conflict. It is an external conflict because it is an argument between Othello and another colliding force in this case another character making it person vs person, with Desdemona. In the scene, Othello is confronting Desdemona about the Handkerchief because Iago has told him he seen it with Cassio and if That is true then its strong proof Desdemona cheated on Othello, What he doesn't know is Iago's wife had brought him the Handkerchief and he had planted it on Cassio. Handkerchief plays a heavy part because it was a gift to Desdemona from Othello and it was believed to keep a couple together with magic. Othello asks Desdemona about the Handkerchief and she is not able to tell him because of course she doesn't have it its been planted on Cassio. Desdemona takes this as an attempt of Othello to push Cassios situation aside however when Desdemona is not able to answer where the handkerchief is it confirms to Othello that she has cheated because she has lost something that important and Iago says it's with Cassio, this forwards the story because it confirms all the doubt in Othello's head and makes him convinced that Desdemona has definitely cheated.
This is the same external conflict Othello has with Desdemona because Othello is conflicting with another character, Person vs Person. however, This is a different Scene and directly changes the path of the story. Previously we know how much Othello loved Desdemona and how he would do anything for her because that's how in love with her he was. In the scene, Othello is building up with anger because he has just received news that he is wanted to go back home and appoint Cassio as Governor as this didn't anger him enough,Desdemona says the worse thing she could've said before the actions depicted in the scene happens she says I'm happy about that and this, Of course, infuriates Othello more because of the thoughts that she has cheated on him and she is even supporting the man she cheated with he calls her insane and slaps her calling her the devil. This is where the story changes when Othello slaps Desdemona because we were introduced to these two madly in love and they couldn't do anything to hurt each other and here Othello just slapped Desdemona which was never before imaginable this shows the impact of this scene on the drama it causes a shift in the character of Othello.
This scene is an example of internal conflict because the character is having a problem with his own mind making it a person vs self-conflict. Iago has planted the seed in Othello's mind that Desdemona has cheated on him and now thinking about the possibility causes him to doubt himself and question his own flaws. You see his true core he is very insecure. He proceeds to question his behavior and then his age and behavior.This is why he is such an easy target to manipulate he is so self-conscious that it's simple to toy with his feelings. This scene plays an important role because its the start of Othello's jealousy developing as he starts thinking he's not good enough and seeks revenge and proof. Along with this Othello is also fueling Iago's plan he wants him to feel like that so Othello ruins himself and tears down his own relationship.