Hi Rahul,

78.73 percentile means that 78.73 students are behind you who appeared for the exam. Your approximate rank can be determined by using the following formula:

JEE Main 2019 rank= (100- NTA percentile score ) X 874469 /100

Therefore Your calculated Approximate rank is 185999.

Whether you have qualified jee mains and are  eligible for jee advance or not will depend upon whether you have crossed the cutoff marks declared by NTA officially. This cutoff will be different for different categories of students. As of now, the cutoff have not been declared and reportedly will be declared after the jee mains exam in April. So better wait for official results.

Good luck