is "share premium" account balance is free reserve?

No sir section 52 restricts the use of SECURITY PREMIUM RESERVE for certain purposes..
Following is the extract of Section 52

2) Notwithstanding anything contained in sub-section (1), the securities premium account may be applied by the company—

(a) towards the issue of unissued shares of the company to the members of the company as fully paid bonus shares;
(b) in writing off the preliminary expenses of the company;
(c) in writing off the expenses of, or the commission paid or discount allowed on, any issue of shares or debentures of the company;
(d) in providing for the premium payable on the redemption of any redeemable preference shares or of any debentures of the company; or
(e) for the purchase of its own shares or other securities under section 68.

no , it is not . the balance from share premium account shall be used for special purposes .

No it is not . However it is a free reserve only for the purposes of Section 68 relating to Buyback