The bar chart shows the time taken for the same mass of four metals to fully dissolve in excess dilute hydrochloric acid. A shorter time means a faster reac...
Question 1 Report
The bar chart shows the time taken for the same mass of four metals to fully dissolve in excess dilute hydrochloric acid. A shorter time means a faster reaction. Which metal is the most reactive?
Answer Details
Rate of reaction with dilute acid is a direct measure of metal reactivity: the more reactive the metal, the faster it releases hydrogen and the sooner it disappears.
Read the bars as time, not as reactivity. The iron bar is the tallest, so iron takes the longest to dissolve; the bars then fall through zinc and aluminium to magnesium, whose bar is by far the shortest. Since a shorter time means a faster reaction, magnesium dissolves fastest and is therefore the most reactive metal shown.
The usual mistake is to pick the tallest bar because "bigger looks stronger". Here the tall bar belongs to the slowest, least reactive metal. Reaction: \( \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \).
Always check what the axis actually measures before ranking bars.
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