Hi,

Yes, you can opt for vocal music for considering as best four subjects. Non-inclusion of economics will lead to a  deduction of 1% marks from the best four aggregate.

If you include any other subject other than subjects available( like vocal music is not there in the list),so it will lead to a deduction of 2.5% marks per subject on the aggregate of best four subjects.

For more information,refer to the website:

https://www.google.com/amp/s/university.careers360.com/articles/du-eligibility-criteria/amp

Best Wishes