The correct answer is option (A), Kaimur.
The sex ratio in Kaimur district is 893 females per 1000 males, which is the lowest among all the districts of Bihar. The sex ratio in Munger district is 912 females per 1000 males, the sex ratio in Saran district is 914 females per 1000 males, and the sex ratio in Madhubani district is 924 females per 1000 males.
The sex ratio is a demographic indicator that measures the number of females per 1000 males in a population. A low sex ratio indicates that there are fewer females than males in the population. This can be due to a number of factors, including female infanticide, gender-selective abortion, and female migration.
Female infanticide is the practice of killing female infants at birth or shortly after birth. Gender-selective abortion is the practice of aborting female fetuses. Female migration is the movement of women out of a particular area, often in search of work or education.
All of these factors can contribute to a low sex ratio. In the case of Kaimur district, it is likely that a combination of these factors is responsible for the low sex ratio.