When some marble chips (calcium carbonate) are heated strongly, substances X and Y are produced. Substance X is a white solid that, when it comes into contact with water, releases heat. Substance Y is a colourless gas. Identify substances X and Y.
- AX: calcium chloride; Y: oxygen
- BX: calcium hydroxide; Y: carbon dioxide
- CX: calcium oxide; Y: carbon dioxide
- DX: calcium sulfate; Y: oxygen