Magnesia (MgO(s)) is used for fire brick, crucibles and furnace linings because of its high melting point. It is produced by decomposing magnesite (MgCO3(s)) into at around 1200oC

Write a balanced equation for the magensite decomposition being sure to include states for the species.

I thought it was:
MgCO3(s) ...> MgO (s) + CO2(g)

but it was marked wrong.

help..thank you.

Probably I would have marked it right; it may be that you omitted the heat sign over the arrow OR the word "heat" on the left side.

To write a balanced equation for the decomposition of magnesite (MgCO3) into magnesium oxide (MgO) and carbon dioxide (CO2), you need to ensure that the number of atoms of each element is the same on both sides of the equation.

The correct balanced equation for this reaction is:

MgCO3(s) → MgO(s) + CO2(g)

It seems that your answer is correct, and the equation you provided is already balanced. However, it's essential to make sure that the states of matter for each substance are correctly indicated, as you have done. The (s) represents a solid, and the (g) represents a gas.

If your answer was marked wrong, it might be due to some other reason or mistake. I would recommend double-checking if there were any specific requirements or instructions provided for the question, as well as ensuring that you correctly transcribed your answer. If you still have concerns, it would be best to consult with your teacher or instructor for further clarification.