Credit for the invention goes not only to edison but also to bell what is the conjunction in the sentence

The answer to your question would be that the conjunction in the sentence is "Not only... but also", a correlative conjunction.

Explanation:

"Not only but also" is a correlative conjunction. What is important about the use of this construction is that the words following both parts of the it should belong to the same parts of speech.  That is, if a verb follows not only, then a verb should also follow but also. In this case, a noun is placed after not only (Edison) and another noun is placed after but also (Bell). Consequently, it can be said the conjunction has been used correctly.

“Not only/but also”

Explanation:

“Not only/but also” are correlatives conjunctions. Correlative conjunctions are those that join sentence elements that are equally important, and that come in pairs but are not placed next to each other, like “Not only/but also” in the sentence which connects Edison and Bell. Other examples of this type of conjunction are both/and, neither/nor, as/as, as many/as, such/that, rather/than and whether/or.

"facing the rising sun of our new day begun

let us march on till victory is won.",

because the rising sun is a symbol of hope.

c) problem and solution