Dissolving sodium chloride in water is a physical change because the chemical composition of the salt (NaCl) and water (H₂O) does not change. The salt ions simply disperse within the water molecules. The original substances can be recovered by physical means, such as evaporating the water, which leaves the solid salt behind. Hence, no new substance is formed, and it is easily reversible.
A. addition of water to calcium oxide is a chemical change. Calcium oxide (quicklime) reacts vigorously with water in an exothermic reaction to form a new substance, calcium hydroxide.
B. corrosion of iron is a chemical change. Iron reacts with oxygen and moisture in the air to form iron oxide (rust), which is a new substance with different properties from the original iron.
D. burning of charcoal is a chemical change. Burning (combustion) involves the reaction of charcoal (primarily carbon) with oxygen to produce new substances, such as carbon dioxide and possibly carbon monoxide, which cannot be easily reversed to get the original charcoal back.
The correct option is C. dissolving sodium chloride in water.
There is an explanation video available below.
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