Dear aspirant,
As per your query you have mentioned total five subjects pcm ,computer science and English so marks of all 5 will be taken for calculating your percentage.
But if you forgot to mention any other subject or if you have 6 subjects in 12 then marks of any best five including pcm and eng will be taken.
Hope you get it.

Dear Aadya, for calculating percentile only compulsory subject is count and your optional subject is not count. As you know PCM, English and one more are compulsory subjects so these are counted when you calculated your percentage. Optional subject is not counted in calculation.