Partners

 all partners must be CA in a Partnership Firm

 SIR IF THE 3RD PARTNER IS CA STUDENT I.E HE HAS COMPLETED HIS ARTICLESHIP BUT HE COULD NOT CLEAR HIS EXAMS AND STILL HE IS STUDENTS IN THE MEAN TIME HE BECAME THE PARTNER OF THE FIRM. EVEN THEN WHETHER HE CAN SIGN OR NOT 

 he cant become a partner still hes CA Student and not the member of the institute

A CA Student who has completed such prescribed period of articleship , qualified relevant exam (CA Final) and holding COP can be a Partner of a CA Firm .

First of all, only partners of the firm can sign the balance sheet - see section 229 of the companies act.

Second, the CA student cannot be a partner.

Third, if he is a partner, then your firm is disqualified from appointment as auditors. Proviso to Section 226 requires that all the partners of the audit firm should be qualified for appointment if the firm is to be appointed. But in this case student partner is not qualified.

thanks G K