Dear Mr.Rajneeth Kumar,
There is no fixed (statutory) percentage for basic whether on CTC or Gross Salary. Basic is basically fixed keeping in mind The minimum wages act 1948 that is laid down by the respective state government and the employment category as mentioned above by Mr. M.V. Kannan.
Conventionally it is around 40% of the Gross salary arrived at, which is very convenient to process PF and other statutory obligations.
Regards,
Shreekanth.P.R