When heated zinc carbonate decomposed to form zinc oxide and carbon dioxide gas how do you knke decomposition is complete

This reaction is characteristic to metal carbonates, which decompose when heated to form the oxide of the metal and carbon dioxide gas.

Explanation:

Just did it...

If the temperature is sufficiently above the decomposition temperature, the mass of the mass will reach a steady level.  When this occurs, the decomposition is complete.  

Explanation:

If you have money and a mass spectrometer, you might consider monitoring the gas space above the zinc carbonate sample for CO2.  Once the sample stops emitting CO2, above the decomposition temperature, you may conclude the reaction has gone to completion.

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of c is as shown here in the image.