IEA- Conditions for section 30

That section itself contains all your query, and the said provisions also says that to bind the co-accused the confessional statements must be proved legally acording to law.

This is not class room  just check with your teacher.

What is the issue? What is the context?

You reminds me of a philosopher Fish. The Philosopher Fish was very sad, when inquire by his wise fellow fishes the reasons of his sarrow, he replied back, "Every where I go, I hear all kinds of fishes talking about the Oceans, so I venture out of my place to see the Ocean, but I coukl not find the Ocean so am sad. 

None of these if the confession is before the police authorities only and moreover not against him also if no recovery has been got effected from the accused confession the offence.

Question is:
A. there must be a joint trial of two or more persons. 
B. the joint trial must be for the same offence. 
C. while the Confession affects the other accused also. 
D. All of these. please explain the answer Sir.
That marginal Section 30 of the IEA reads as under:-
Section 30. Consideration of proved confession affecting person making it and others jointly under trial for same offence……………………………………..

The answers to all your questions are there in the marginal portion of that Section 30 itself. As pointed out by Sir. Raj Kumar Makad, Section 25 and 26 of the Indian evidence Act, prohibits any statements made in police custody or before police officer by the accused, but any materials so discovered by such statements by the accused may be used as evidence against the accused, but such material discovery cannot be used against the co accused, either under Section 27 or Section 30, of the Indian evidence Act, as an accomplice is regarded as unworthy of credit. But there are certain statements of accused which can be used against the co-accused, if such statements are made according to law and proved in the court. In this connection you may also refer to Section 306 CrPc.