I have to apply for Gate exam under General-EWS category .what of I will unable to show certificate at the time of admission
If you are looking to get benefits of the 10% relaxation at the time of admission, it's imperative that you arrange for the certificate beforehand. If you are unable to produce this certificate at the time of admission, you will not be allowed to take the benefits of the category. Try to arrange for the certificate, there's ample time for the same.
Hope this helps.