It had a manufacturing defects. There were 4 capacitive button. 3 of them(Google search, Home and Back button) had backlight problem as they didn't light up if touched but the forth one(multitasking key) located far left had backlight.
I went to their service center they kept for 2 months and after that when they return it issue was not solved. I reported immediately they again took it back and and send it for repair and kept for 5-6 months. Even after that issue was still not solved. And now the screen and back panel was full of scratches and they refused to accept that these scratches were there because of their fault. They pretend that I scratched the phone before bringing it to service center. So finally I had two issues No backlighting and a phone with full of Scratches. Though initially I had only had the backlighting problem.
Anyway lesson learned. Finally Flipkart exchange my Karbonn phone and bought Redmi 2 prime :s
Till now I'm used 5 phones. First Reliance CDMA (ZTE brand) then Nokia 1209(now my mom using this) then Maxx mobile MX444 (still working) then Nokia 2700 Classic (awesome phone & still working) Now using Asus ZenFone Go...:tup