As per Indian law, if you are asked to worked on national holidays, you either get a compensatory off or you are eligible to get double the pay. You can discuss with your manager. Only certain professions like emergency services/ public utilities etc are exempt from it. Make sure you mark your attendance on that day and keep a written record of it, in case it is disputed that you called to work in office.
On a side note, if you want to say No, just mention being a long weekend, you already made plans. Tickets are booked, and if cancelled, your manager should comp you for it.
There are N number of ways to politely decline. Figure out the best as per your situation.
Lastly, working on weekend is always a favor you are doing. If your manager is being polite and requesting it, then consider it. If he is ordering around, well then, its best to look for a change in team/project/org.