Sir I pass 12th in 2015 sit for jee not selected in 2015 and selected forjee main in 2016 is I am eligible for jee main and advanced 2017

@VAIBHAV 
yes , for that u need to qualify jee main 2017 frst , only then u are elligible , 
but the jee main 2016 marks will no more valid for 2017 . and jee adv have 2 attempots max , so, this will be your last attempt . u will not be elligible after thgis attempt . 

HOPE IT CLEARS 
ALL THE BEST ..