Option 1: Paper is biodegradable as it is made from wood pulp, which can decompose naturally. Grass is also biodegradable as it can naturally break down into organic matter. However, glass is not biodegradable as it is made from sand and does not decompose naturally.

Option 2: Wood is biodegradable as it can decompose naturally. Flowers are also biodegradable as they can break down into organic matter. However, iron scrap is not biodegradable as it is a metal and does not decompose naturally.

Option 3: Sewage is partially biodegradable as it contains organic matter that can decompose over time. However, plastic is non-biodegradable as it is made from synthetic materials that do not decompose naturally. Leather is partially biodegradable as it comes from animal hide, but it is often treated with chemicals that make it less biodegradable.

Option 4: Cow dung is biodegradable as it is organic matter that decomposes naturally. Paddy husk is also biodegradable as it comes from rice and can decompose naturally. Vegetable waste, such as leftover food scraps, is biodegradable as it can break down into organic matter.

Therefore, option 4 contains only biode