Concept: Plastics are long-chain polymers held together by strong covalent bonds. These bonds are very stable and resist breakdown by natural processes.
Explanation: Plastics are made of carbon‑based molecules linked by strong covalent bonds.
These bonds are not easily broken by water, air, or microorganisms.
This makes plastics durable and non‑biodegradable.
Option A: Ionic bonds are found in salts, not in plastics. Ionic compounds can dissolve or react easily.
Option C: Metallic bonds occur in metals, giving them conductivity; plastics lack such bonds.
Option D: High melting point is a property, not the cause of non‑degradability. The core reason is the strong covalent bonds that cannot be attacked by microbes.
Thus, covalent bond strength is the primary reason plastics persist in the environment.
Answer: B. They have strong covalent bonds.