Whatsapp has been blocked in our country.
I know what you are thinking but it's true.
So is there anyway I can still use whatsapp by vpn?
(for android)

Yes, if you use a VPN then you can access websites blocked by various nations. The VPN just needs to connect though a location that allows access

Do you know any name of vpn app (android) that
1. allows me to change country
AND
2. allows me to block net access for individual apps.
Please tell me.
By the way MY PHONE IS ROOTED.

What country are you in? I use different ones, Most are good, I use fqrouter on my phone, and I use pandapow on my computer. I am in China and they almost always get me past the national firewall

I live in Bangladesh.