is it Mandatory to provide interest On capital in Partnership Firm

it is not mandatory but normally this clause is put in the deed.
you can provide it in the deed the amount of remuneration ad decided mutually amongst all the partners.
however under IT remuneration wud be allowed subject to the limits specified under section 40(b)
on first 3lacs 150000 or 90% of book profits whichever is high
and balance book profits 60% is allowed

If remuneration is mentioned deed then how to increase salary every year that also we need to mention or is it fixed

you can mention either the amount and put a clause like increase in remuneration after every 4years . or just put a clause like remuneration to be paid to partners as mutually agreed between all of them subject to increase