Explain why oxygen concentration falls in the tubes

Oxygen concentration is the primary factor that controls NOx during the devolatilization process, and reducing conditions during devolatilization favor the formation of N2 instead of NOx. The residual char left after the initial devolatilization steps burns more slowly than the volatiles, and the corresponding slow rate of char nitrogen conversion to NO is difficult to control

The right answer is b hydrogen bonds!

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