On passing carbon dioxide through limewater, the lime water turns milky. This is due to the formation of.

1. ${\mathrm{CaCO}}_3$
2. ${\mathrm{Na}}_{2}O$
3. ${\mathrm{Na}}_2{\mathrm{CO}}_3$
4. $\mathrm{CaO}$

The correct option is A ${\mathrm{CaCO}}_3$
When carbon dioxide is passed through lime water, it turns milky due to the formation of calcium carbonate (${\mathrm{CaCO}}_3$) which is a white precipitate.
$\mathrm{Ca}(\mathrm{OH}{)}_2+{\mathrm{CO}}_2\to {\mathrm{CaCO}}_3+H_{2}O$
When excess carbon dioxide is passed, the milkiness disappears due to the formation of calcium hydrogen carbonate which is highly soluble.
${\mathrm{CaCO}}_3+H_{2}O+{\mathrm{CO}}_2\to \mathrm{Ca}({\mathrm{HCO}}_3{)}_2$