Buy back of shares can not be done out of the following sources:

The correct answer is Option (4) → Existing Debentures holders

Under Section 68 of the Companies Act, 2013, a company may buy back its shares from existing equity shareholders proportionately, from the open market, from odd-lot shareholders or from its employees. Debenture holders hold no shares, so there is nothing to buy back from them.

Option (1) Open Market — A true statement. It is listed as a source in Section 68.

Option (2) Odd lot shareholders — A true statement. It is listed as a source in Section 68.

Option (3) Employees of the company — A true statement. It is listed as a source in Section 68.