Hi

You need to mention 2016 as your 12th passing year.

This is because ,

it doesn't matter even if you're have appeared for improvement examination in 3 subjects in 2017 but your passing still remains the same
as you you had already passed your 12th board examination in 2016 itself and just to improve or increase your percentage you  had appeared in  improvement examination.

In case if you are going to take admission in graduation then to help you in deciding the course you should choose after your 12th you can go through our page for  which link is provided below
https://school.careers360.com/articles/courses-after-12th

In case if you have any other doubts then do let us know so that we can help you with relevant information.

Thank you