is that so

Is that really true? Is that a fact? Can be used to indicate simple acknowledgement or surprise, or sarcastically to indicate disbelief. A: "John's got the flu so he'll have to skip this week." B: "Is that so? That's too bad. Tell him I hope he feels better." A: "I'm actually a black belt." B: "Is that so? Wow, I never knew you were so highly trained." A: "I'd be rich if J.K. Rowling didn't steal my idea!" B: "Oh, is that so? Gee, too bad for you."

Is that so?

and Is that right?

1. Is what you said correct? (With rising question intonation.) Henry: These are the ones we need. Andrew: Is that right? They don't look so good to me. Fred: Tom is the one who came in late. Rachel: Is that so? It looked like Bill to me.

2. That is what you say, but I do not believe you. (No rising question intonation. Slightly rude.) Mary: You are making a mess of this. Alice: Is that so? And I suppose that you're perfect? Bob: I found your performance to be weak in a number of places. Henry: Is that right? I suppose you could have done better?

is that ˈso?

(informal)
1 used for telling somebody that you are not frightened by their actions or threats: ‘If you don’t shut your mouth I’ll kick you out of the house.’ ‘Is that so? You just try it!’
2 used to express surprise or interest at what somebody has said: ‘He owns twenty cars.’ ‘Is that so?’