Final answer:
The ratio of sigma to core before elongation in E. coli RNA polymerase is 1:1, and during the elongation phase, 100% of RNA polymerase core enzymes are actively elongating as sigma factor detaches after initiation.
Step-by-step explanation:
The correct ratio of sigma to core in prokaryotic RNA polymerase and the percentage of RNA polymerase that is actually elongating is found in option C. In E. coli, the core enzyme is made up of four subunits: two alpha subunits, one beta subunit, and one beta prime subunit. The sigma factor (σ), which is necessary only during the initiation phase of transcription, is the fifth subunit that temporarily associates with the core enzyme to form the holoenzyme. Once initiation is complete, sigma factor detaches, and the core enzyme proceeds with the elongation phase of transcription. This disassociation implies that there is generally one sigma for every core enzyme that initiates transcription, but since sigma detaches after initiation, only the core enzymes are involved in elongation.
As a result, although the ratio of sigma to core enzyme initially is 1:1, during elongation the active RNA polymerase (core enzyme without sigma factor) is 100%, thus none of the RNAP is associated with sigma during elongation, contradicting all the options provided in the question.