**Core Concept**
The mid-day meal programme aims to provide nutritionally adequate meals to school-going children, primarily focusing on the energy and nutrient requirements for growth and development. The meals must be designed to meet the dietary needs of children in different age groups, taking into account their energy expenditure and nutrient requirements.

**Why the Correct Answer is Right**
The correct answer is based on the principle of providing 50% of the recommended daily allowance (RDA) of calories and nutrients. This allows children to meet their daily energy needs while also providing essential nutrients for growth and development. The meals should be designed to provide a balanced mix of carbohydrates, proteins, and fats, along with essential micronutrients like vitamins and minerals.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify the percentage of RDA that the meals should provide. While meals should be nutritious, simply stating "adequate" is not sufficient.
* **Option B:** This option is incorrect as it implies that the meals should provide 100% of the RDA, which may be excessive for children's energy needs and may lead to overconsumption of calories and nutrients.
* **Option C:** This option is incorrect as it does not provide any specific guidance on the nutritional content of the meals, making it vague and unhelpful.

**Clinical Pearl / High-Yield Fact**
To ensure that the meals provided in the mid-day meal programme are nutritionally adequate, it is essential to involve a multidisciplinary team of experts, including nutritionists, pediatricians, and food scientists, to design the meal plans and monitor their implementation.

**Correct Answer: D. 50% of the RDA of calories and nutrients.**