Forensic Science

The biggest criterium will be biology, in order to complete a Forensic Medical Science course, particularly those that are focused on medico-legal studies.
In some Bachelor programs, a BSc Forensic Science programme may accept PCM (Physics, Chemistry, Math) students, depending on the institution. But in terms of Diploma or forensic medicine related courses, and so forth, PCB is the wisest choice.

They are two distinct career pathways. An Forensic constitutes a doctor, whereas Forensic Medical Science trains you as to where you fit in the medico-legal and investigative space. One is focused on treatment of patients, and the other is based on solving a criminal case using medical science.
If you liked medicine and law; forensic medicine (after MBBS) is a hybrid of both. However, if you are more interested in criminal investigation, using science, then forensic Science may suit you better.

For Forensic Medical Science, I suggest that you try viewing forensic shows in real life or reading forensic medico-legal case studies or, if you can, shadowing someone in the profession. That is a taste of the reality of the profession.
Passions often manifest when you are curious to learn and growing your expertise, free of pressure, and still excited when having an understanding of what is tough – like post-mortems, or lengthy legal processes.

If you are interested in science, crime solving, and the legal system, then Forensic Medical Science is right for you. Forensic Medical Science is a good fit for analytical thinkers who enjoy a scientific approach to biology and deduction.
You may also want to be comfortable with medical or forensic specifics like autopsies or injury reports. If that does not scare you and may excite you, then you may have find your field.

Definitely college ranking is significant, but remember ranking is not the end all be all, especially in specialised areas like Forensic Medical Science. 
What is more crucial is the institution's exposure to the profession, laboratory facilities, and rapport with industry partners. 
Having attended a lesser-known college with forensic programs and good placement assistance is better than attending a top ranked college with less specialisation in forensic science. 

Yes, many colleges may admit students for UG Forensic Medical Science based on Class 12 results in any human Science (science stream). You can see on their websites what there admission to Diploma or undergraduate courses on forensic medical Science will be without the need for an entrance exam. 

That said, there may be some reputable universities (or postgraduate programme) that may require you to take an internal exam or interview, so please carefully look at the eligibility when considering application to the institute.

A new graduate just after BSc in Forensic Science can grab a fresher-level salary somewhere between INR 3 Lacs and INR 5 Lacs per year. The average salary may vary on the factors like real time industry standards, job market, job role, and skill set of the individuals. The potential job roles that can be expected after pursuing BSc Forensic Science are - forensic scientist, crime scene investigator, forensic analyst, and forensic psychologist. In addition to that opportunities exist in areas like forensic pathology, anthropology, and digital forensics as well.