Select the correct idiom to fill in the blank in the following sentence:-

We were talking ______. I was talking about the exams, and you thought I meant the course as a whole.

at cross purposes

The correct answer is Option (1) : at cross purposes*

• At cross purposes means that two or more people believe that they are discussing the same topic, but they are actually talking about different things, resulting in a misunderstanding.

The example perfectly illustrates this: one person's intent (exams) was misunderstood by the other (the whole course).

• To some purpose: Means with a useful or successful result.

• In the dark: Means unaware or uninformed about the relevant facts.

• Out of the loop: Means not part of a group that is kept informed about something.

None of the other options relate to the specific issue of discussing two different subjects simultaneously.