From LimeSurvey Manual
Exclusive option (exclusive_option)
The exclusive option attribute takes the code of an answer in a multiple option question so that when clicked on its corresponding checkbox, all the other previously checked options will get unchecked and get marked as read-only (=disabled). This function was created to ensure the data integrity when one of the multiple options in a multiple option question implies that no other option can be selected too. Basically, this feature marks the other attributes as being irrelevant.
For a short explanation on answer codes, check first the following wiki section. Once understood, introduce the "AnswerCode" that will trigger the function once selected.
Below, you may see an example where the exclusive option attribute is used.
You can see in the first screenshot that some non-LimeSurvey options are selected:
If you click on the marked option (which is entered in the exclusive option box), the other options will get unmarked and disabled, being left only with the current option checked:
To take a closer look at our example, import the .lsq file into your LimeSurvey installation: