**Core Concept**
The question tests the knowledge of nutritional requirements in adults, specifically calorie and nitrogen needs. The correct answer involves understanding the estimated daily energy expenditure and protein requirements for a sedentary adult.

**Why the Correct Answer is Right**
A sedentary adult requires a daily calorie intake of approximately 120-150 kcal/kg/day to maintain basic metabolic functions. This estimate is based on the basal metabolic rate (BMR) and is adjusted for physical activity level. The correct answer aligns with this understanding. Nitrogen is a crucial component of amino acids, which are the building blocks of proteins. The body's nitrogen requirement is estimated to be around 0.6-0.8 grams per kilogram of body weight per day, not 1 gram/kg as mentioned in option C.

**Why Each Wrong Option is Incorrect**
**Option A:** This option significantly underestimates the calorie needs of a sedentary adult, making it an incorrect choice.
**Option C:** The specified nitrogen requirement of 1 gm/kg is higher than the actual recommended amount, making it an incorrect option.
**Option D:** The statement that one gram of nitrogen yields 6 grams of protein is incorrect, as it actually yields approximately 6 grams of amino acids, not protein.

**Clinical Pearl / High-Yield Fact**
A commonly used estimate for protein requirements in adults is 0.8 grams per kilogram of body weight per day, which can be adjusted based on factors such as age, sex, and physical activity level.

**Correct Answer: B. Daily calorie intake in a sedentary adult is 120-150 kcal/kg/day.**