What happens to the yolks of eggs cooked over hard?

When eggs are cooked over hard, the yolks are broken and fully cooked, resulting in a firm texture. This cooking method entails flipping the eggs after they begin to set, which causes the yolks to break and blend with the whites. Thus, the yolks become solid and take on a more opaque appearance as they are heated thoroughly.

The other options do not accurately describe the characteristics of yolks in over-hard eggs. They do not remain soft, nor are they left whole, as the action of flipping breaks the yolks. Additionally, cooking sunny-side up refers to a method where the egg is cooked on one side without flipping, which preserves the runny quality of the yolk, contrasting with the fully set and broken yolks of over-hard eggs.