As you have asked about the joint Entrance Exam (JEE) Mains candidate login to view answer key, I am giving you information about it, check below for the details

For that you can follow steps given below
Go to JEE Mains website

Here you will see

View/Challenge - Answer Key of Paper 2
View/Challenge of Recorded Responses of Paper 2
JEE(Main)-2016 Score of Paper I

Click on View/Challenge - Answer Key of Paper 2, the page open look like



Here enter your details like
Application Number :
Date of Birth :
Enter Security Pin (case sensitive)

Then click on Login.
You will be able to login.