Which of the following changes is an example of a chemical change?
A. Melting of ice
B. Boiling of water
C. Dissolving sugar in water
D. Burning of magnesium ribbon
Answer: Option D
Solution (By JKSSB Mock Tests)
Burning of magnesium ribbon produces a new substance, magnesium oxide (MgO), and releases heat and light, which are indicators of a chemical change. Melting, dissolving, and boiling are physical changes because the chemical composition remains unchanged. Chemical changes are generally irreversible.
Explanation:
Neutralization is a chemical reaction in which an acid and a base react quantitatively with each other to form a salt and water. For example, HCl + NaOH → NaCl + H₂O. It is generally an exothermic process, and the resulting solution has a pH closer to 7.
Explanation:
PVC (polyvinyl chloride) is a polymer of vinyl chloride (CH₂=CHCl). It is used in pipes, electrical insulation, and flooring. It can be rigid (uPVC) or flexible with plasticizers. It is a thermoplastic. Chlorate/carbon/carbide are not correct expansions.
Explanation:
Flooded rice paddies promote anaerobic decomposition of organic matter, producing methane (CH₄). It is a potent greenhouse gas. Livestock also emit methane.
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