Why do plastics not degrade easily ?
- A.They have strong ionic bonds.
- B.They have strong covalent bonds.
- C.They have strong metallic bonds.
- D.They have very high melting points (> 500°C).
Correct answer
Explanation
The correct answer is B, They have strong covalent bonds. Plastics are long chains of carbon atoms joined by strong covalent bonds, which water, air and most microbes cannot easily break.
A plastic such as polythene is a polymer: thousands of small units (monomers) linked into a long chain by carbon–carbon and carbon–hydrogen covalent bonds. Bacteria and fungi have evolved enzymes to break natural polymers like starch and cellulose, but very few can attack these synthetic chains. So plastics are non-biodegradable and can last for hundreds of years in soil and oceans, which is why their disposal is a major pollution problem.
Option A is wrong because plastics are not ionic compounds. Option C is wrong because metallic bonds are found only in metals. Option D is wrong because most plastics soften or melt well below 500°C; many melt between about 100°C and 300°C.
Exam tip: plastics are covalent polymers and non-biodegradable; thermoplastics soften on heating, thermosets do not.
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