Yes with 98% marks in 12th one can easily get Jadavpur university but it also depends on what branch he is trying for. Students with 98% in 12th have merit numbers below 200.
For CSE and IT branches, the seats are filled below 150 merit numbers usually and for the EnTC branch students with merit numbers, less than 300 get the seats. For electrical, chemical, and Instrumentation your merit should be below 600.
For civil and mechanical there is less competition in Jadavpur University. It is been observed that student with merit number 2306 has also got CIVIL Engineering under PMSSS.