Naphtha yield in straight run distillation of crude oil may be about __________ percent.

Answer: Option D

Naphtha is a major light fraction obtained from straight run (atmospheric) distillation of crude oil.

The yield of naphtha depends on crude oil type, but for an average crude, it typically lies in the range of 15% to 20%.

Thus, 18% is the most appropriate and representative value among the given options.

Lower values such as 2% and 6% are too small and correspond more to lighter gases, while 12% may occur for heavier crudes but is below the common average.

Therefore, the correct answer is 18%.