The correct answer is option 3: scale leaves. In onion plants, the edible part is actually composed of modified leaves, specifically known as "scale leaves." These scale leaves provide protection to the inner layers of the onion bulb, allowing it to store food. Unlike typical leaves, which are green and photosynthesize, scale leaves are dry and papery and serve the purpose of storing nutrients. They surround the fleshy layers of the onion bulb, which contain the stored food. Therefore, option 3 is the correct answer as it correctly identifies the part of the onion where food is stored.