Which of the following oxides, when dissolved in water, produces a solution with a pH greater than 7?
Show the answer and explanation
Correct answer
C. CaO
Principle or equation
Metal oxides are basic; they react with water to form bases (e.g., CaO + H2O -> Ca(OH)2). Nonmetal oxides are acidic; they form acids (e.g., CO2 -> H2CO3, SO2 -> H2SO3, P2O5 -> H3PO4).
Why this answer is correct
CaO is a metal oxide and reacts with water to form calcium hydroxide, a strong base, giving a basic solution (pH > 7). The others are nonmetal oxides that form acidic solutions.
Example
Na2O + H2O -> 2NaOH, producing a basic solution.
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