Discussion
A metal X burns in oxygen with a white flame to form a white ash. Identify X and the type of reaction :
Answer: C
X is magnesium (Mg), and the reaction is a combination reaction.
Magnesium ribbon burns in air with a dazzling white flame and leaves a white powder, magnesium oxide:
\[ 2\text{Mg} + \text{O}_{2} \rightarrow 2\text{MgO} \]
Two substances join to form one product, which is the definition of a combination reaction (it is also exothermic, not endothermic). Burning is never a decomposition, which splits one substance into several, so the calcium and aluminium options fail on the reaction type, and burning zinc is exothermic, not endothermic, and does not give the dazzling white flame described.
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