- Neither Raman nor Mohan nor David was ready to come.
- Either the teacher or the students write on the blackboard.
- Either the students or the teacher writes on the blackboard.
- Either the students write on the blackboard or the teacher does.
Are all these sentences OK?
The third one is incorrect. Since you are talking about both the students and teacher you need to use a plural verb, well at least that is what I think lol.
The sentence is not talking about both the students and the teacher, it’s talking about either the students or the teacher. In cases like this, a common convention is to have the verb match the closest noun.