5.
I dont think exception are applicable in your case. still for your information
In General, If your Output service is exempted from tax in this case you cant get the input of the service.
if your input service is not in relation with the output service in that case you again are not entitled for the input credit.
So yes you can get the Input on 75 percent on basis of Invoice,25 percent on basis of Challan
Note: you have to deposit 25 percent first, you cant adjust your input against this amount of 25 percent .