Hi Sourabh,
Firstly you cannot create a condition without a value for a field (Department). However, if you select a value for field (Department) then it is possible to fulfill your requirement.
You can use Document choice functionality for full project template only
Steps to create Document Choice:-
1. Go to Document tab in your full project template
2. Action-->Create Document Choice
3. Enter Name & Description
4. Select 'Event' for Type Field
5. Under Add Choice area add your template A & B. Define condition for both the template.
Now, while creating a event you will only find the template under document choice which satisfy the condition.
I hope this will help you.
Cheers!!
Aditya