I am currently in Xth grade. I will give SAT this year in May and am aiming for a score of 1470-1560 types. I want to apply to UIUC,UCBerkeley,Harvard,Yale,Stanford and GeorgiaTech.Can someone review my ECs??
-Founding Member of Quiz Club in School.
-Conducted an intra(selection test) for junior members by making a quiz and organizing the event.
-Have been the winner of Dorling-Kindersley Quiz from my School.
-Was a part of the 10-member school team sent to interschool maths competitions.(twice)
-Have qualified the SMTE exam and been invited to attend two week-long camps
-Have cleared the JSTSE exam and will receive the scholarship.
-Have been the winner of Postal Quiz Competition organized by postal branch of our government.
-Winner of the Ecomm-Matrix Buzz(Interschool Event) in a play.
-Have a GPA of 9.8,9.9/10 in school.
-Was sent to represent the school at various quizzes like Thailand Quiz,Columba Quiz,INTACH etc.
-Part of the 10-member team of my school for Korean Quiz.
-Was sent to Ramanujan Inter-school math contest as a part of a 10-member team which won the 1st prize.
so is this sufficient or i need more? and how much more ?
You sure do love quizzing! You EC’s are great. Being a founding member and organising events shows great amounts of responsible and leadership qualities in you. I don’t think your GPA would be part of this list. It would be covered when your giving details about your academics.
Anyway, to answer your question if this is sufficient - well, it is more of you trying to show what your passionate about. If the list comprises everything you are deeply and truly involved in, your good to go! I’m not sure if you are aware, but Stanford and Gatech both use a portal called Common Application for you to submit your application through. For this, you can submit only upto 10 ECs, which you’ll have to write in order of importance to you. Each activity requires a description of what you have accomplished by doing this and any recognition that you have received. I’m not sure about Harvard and Yale. UCBerkely and UIUC both use their own websites. They use a similar system as well but I don’t think they have a limit on how many you can enter. I know for sure that the UIUC application has a section called “Honors and Recognition” where you have a chance to enter any distinction and awards that you have received. So maybe some of yours would belong there. Also, if you go to classes, like some sports training, music classes or any clubs or if you’ve performed at an event like a Concert, talent show, et cetera, regardless of whether it is within your school or not, also count towards these ECs.
Use your EC section to give the admission officers a gist of you outside the classroom. Who are you apart from your academics? What are your deep lying interests? What do you, as an individual, add to this community? UCBerkeley, Harvard, Yale and Stanford are one of the pickiest. They look for a lot of uniqueness in you. They try to pick students that create a vibrant classroom. Gatech is slightly less pickier, and UIUC, in your list, the least. (It is picky, but just not as much as the others you have mentioned) There are more opportunities for you to express yourself in the application which is through your essays.
I wish you the best for your future, and I hope you get into these places! They are truly amazing! 
I really didn’t see the topic of the question, haha. Ummm, the Major you will get depends on many factors. There is no stringent methodology to do that. What do you want to do, though? Now, UIUC looks at the major you have applied for and sees if your competitive enough along with all the ECs and essays. While this is true for other universities, they might not necessarily see if your competitive just for your major, but competitive in general. Again, as I said, universities in the US do a holistic review of your application. Those SAT scores that your aiming for are terrific, but many universities really care if you can show the passion that you have for what you do.
This list might get you into these universities, but it is dependant in many other things. Only admission officers can decide.
Articles to read:
1.) http://mitadmissions.org/blogs/entry/there_is_no_formula
2.)http://mitadmissions.org/blogs/entry/floating_on_a_whim
3.)http://blog.prepscholar.com/how-to-get-into-harvard-and-the-ivy-league-by-a-harvard-alum
4.) https://alumni.stanford.edu/get/page/magazine/article/?article_id=66225