Which of the following oxides is soluble in water?
- AFeO
- BZnO
- CCaO
- DMore than one of the above
- ENone of the above
Show answer and explanation
Correct answer: (c) CaO
Explanation
Calcium oxide (quicklime) reacts with water, giving off much heat, to form calcium hydroxide, which dissolves a little to give limewater:
CaO + H₂O → Ca(OH)₂
So among these it is the oxide that counts as soluble. FeO and ZnO do not dissolve in water.