## **Core Concept**
The sex ratio is a demographic measure that represents the number of females per 1000 males in a population. It is an important indicator of the gender balance within a given area or community. The sex ratio can provide insights into social, economic, and cultural factors affecting a population.

## **Why the Correct Answer is Right**
The correct formula for calculating the sex ratio is: (Number of females / Number of males) * 1000. This means that if you have the number of females and males, you divide the number of females by the number of males and then multiply by 1000 to get the sex ratio. For example, if there are 550 females and 500 males, the sex ratio would be (550 / 500) * 1000 = 1100.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it suggests the number of males per 1000 females, which is the inverse of the standard definition of sex ratio.
- **Option B:** This option is incorrect because it does not specify the correct relationship or formula for calculating the sex ratio.
- **Option D:** This option is incorrect because it suggests a ratio of males to females without specifying the standard multiplier of 1000.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that a sex ratio of 1000 indicates an equal number of males and females. A ratio greater than 1000 indicates more females than males, and a ratio less than 1000 indicates more males than females. In many countries, the sex ratio at birth is slightly skewed towards males, but societal factors can lead to variations.

## **Correct Answer:** C.