Final answer:
The RDA for vitamin C for adults is 70 mg per day, with citrus fruits being one of the richest natural sources.
Step-by-step explanation:
The Recommended Daily Allowance (RDA) for vitamin C for adults is 70 mg per day. This nutrient is crucial for various bodily functions, including the absorption of iron and the reduction of the duration and severity of the common cold. Citrus fruits like oranges and lemons are potent sources of vitamin C, as well as other foods such as green vegetables, cabbage, guavas, berries, melons, and tomatoes.