Hope you are doing good.

Yes many private colleges use this tactic to ensure your admissions into their colleges.

what you need to understand that they are not actually providing admissions to the candidates they are just reserving seats.

If a candidate fails to qualify any of the 12th exam his admission would be cancelled.

private colleges offer lucrative discounts for pre booking that's why many students apply for pre booking.

If you want you can also join colleges through this method. If you are confident about passing your biology exam you can try this out.

if you have any more doubts you can ask them in the comment section I would be more than happy to help you.