Which of these changes produces a chemical change? O A. A stone fizzes and forms a gas when acid is dropped on it.
B. Limestone slowly dissolves in water and forms a cave.
O C. Lava cools and changes from a thick fluid to solid rock.
OD. A large rock is crushed into gravel.

Explanation:

Limestone (CaCO3) dissolves in water - with difficulty - but remains, and can be recovered as CaCO3

Solidifying lava and rock crushed to gravel are physical changes.

If acid dropped on a rock causes fizzing and gives of gas, that is a chemical reaction, e.g,

CaCO3 + 2HCl —> CaCl2 + H2O + CO2

Dissolution of limestone in water does result in dissociation into ions that may be hydrated, but CaCO3 is precipitated out as solutions become more concentrated.

CaCO3 + 2H2O —> Ca++ + CO3= + OH- + H3O+

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