Enable answer or validation rule

HI
I WANT TO PUT A CONDITION OF VALIDATION ON A YES / NO TYPE QUESTION
Modality1

Modality2

I want that if we check the yes of modality 2 that the interviewer cannot choose modality 2 in other words it displays an error

What is a ‘modality’?
How is ‘Modality1’ relevant to the question?

just a variable

Var1
Var2

how is modality 1 relevant to the question you are asking?