If you search for “unread” mails you will get mails that are in all the tabs.
The search query you have to use is:
is:inbox -category:(updates OR promotions OR social OR forums) is:unread
As seen on: http://techwelkin.com/search-unread-emails-primary-tab-gmail
HolaRails 
THANK YOU! this is exactly what I needed!
You can also use:
is:inbox category:primary is:unread
or even just
category:primary is:unread
Easiest way for primary unread is, ” is:unread category:primary “
Why not this?
is:inbox category:(primary) is:unread
Oh My Gee! Spot on! Exactly what I need. TY so much!
Thanks for guiding on how to filter unread emails in primary tab!
Thank you that what I was looking for too.
you can use this query too : category:primary is:unread
category:primary is:unread