Question

By squeezing lemon on a piece of rock the gas liberated turned lime water milky which compound is present in the rock

Answer 1

Hey mate,

This means it contains CO2 ( Carbon dioxide ).

This is because insoluble calcium carbonate that is CaCO3 is formed.

hope this helps you out!

Answer 2

CaCO3 is present in the rock when it reacts with lemon in which citric acid is present it forms CO2, H2O and salt.
And due to presence of Co2 it turns lime water milky