To determine which of the reactions represent a chemical change, let's analyze each option:
A. Heating a solid ammonium chloride in a test tube - This typically does not represent a chemical change. Ammonium chloride can sublime upon heating, changing from solid to gas (ammonia and hydrogen chloride), but it does not result in a new substance.
B. Putting ink on a filter paper - This represents a physical change. The ink spreads on the filter paper, but the chemical composition of the ink doesn’t change.
C. Burning a candle in air - This represents a chemical change. When a candle burns, the wax (a hydrocarbon) reacts with oxygen in the air, producing carbon dioxide, water vapor, and heat.
D. Adding sodium chloride in water - This is a physical change. Sodium chloride (table salt) dissolves in water, but it does not change chemically; it remains sodium and chloride ions in solution.
Based on this analysis, the reaction that represents a chemical change is:
C. Burning a candle in air.
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