Hello, Hope you are doing well,

Here is the answer to your question, NCERT Social Studies of class XI and X are enough to make you an NTSE scholar. For Maths and Science section refer to THM'S NTSE Guide. It is advised to you to refer state board books and previous year question papers. Regarding online education, M Learning India is the best website. They provide you with 1TB of the hard disk of study material which is best in the market. You can even go to their website for offline lectures and course details. Hope I have cleared your query.

I think it helps you!!!

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Wish you good luck!:)