## Core Concept
Human milk is a rich source of essential nutrients for infants, including calcium, which is crucial for the development of bones, teeth, and various physiological functions. The concentration of calcium in human milk is an important factor for infant nutrition.

## Why the Correct Answer is Right
The correct answer states that calcium in human milk is approximately 30 mg/100gm. Human milk typically contains about 30-35 mg of calcium per 100 ml. This concentration supports the infant's rapid growth and development, particularly in the formation of the skeletal system. The bioavailability of calcium in human milk is also high, making it an ideal source for infants.

## Why Each Wrong Option is Incorrect
- **Option A:** 10 mg/100gm - This is too low compared to the known concentration of calcium in human milk.
- **Option B:** 20 mg/100gm - This is lower than the established concentration of calcium in human milk.
- **Option D:** 40 mg/100gm - This is slightly higher than the generally accepted concentration of calcium in human milk.

## Clinical Pearl / High-Yield Fact
A key point to remember is that breastfed infants have a lower risk of developing conditions related to calcium imbalance, such as rickets or hypocalcemia, due to the optimal composition of human milk. The calcium content in human milk is one of the reasons why breastfeeding is highly recommended for infants.

## Correct Answer: C. 30.