what is the minimum cutoff marks and vacancies for instrumentation??
Are we talking of recruitment through GATE? If yes, please refer to this article - GATE cutoff for PSU recruitment . This gives all the past year cutoff marks and you can get an idea. As for the vacancies, I am afraid you should check the complete PSU list that is recruiting. To do so, check PSU recruitment through GATE 2018 article.
The list of top colleges to study Instrumentation Engineering is: