Answer: C
Na + O2 →Na2O
Step-by-step explanation:
A
MgCO3→MgO + CO2 balanced
B
NaCl + KI →NaI + KCl balanced
C
Na + O2 →Na2O not balanced the balanced would be 4Na + O2 →2Na2O
D
Ca + MgSO4→CaSO4+ Mg balanced
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