**Metal Oxide Formation on Heating**

Metal oxides are compounds formed by the reaction of a metal with oxygen. When certain metal compounds are heated, they undergo decomposition and form metal oxides. Among the given options, the metal compounds that form metal oxide on heating are:

**A) Na2CO3 - Sodium Carbonate**
When sodium carbonate (Na2CO3) is heated, it undergoes thermal decomposition to form sodium oxide (Na2O) and carbon dioxide (CO2). The reaction is as follows:
2 Na2CO3(s) → Na2O(s) + 3 CO2(g)

**B) Li2CO3 - Lithium Carbonate**
Lithium carbonate (Li2CO3) also undergoes thermal decomposition when heated to form lithium oxide (Li2O) and carbon dioxide (CO2). The reaction is as follows:
Li2CO3(s) → Li2O(s) + CO2(g)

**C) K2SO4 - Potassium Sulfate**
Potassium sulfate (K2SO4) does not directly form a metal oxide when heated. Instead, it undergoes thermal decomposition to form potassium pyrosulfate (K2S2O7) and sulfur trioxide (SO3). The reaction is as follows:
2 K2SO4(s) → K2S2O7(s) + SO3(g)

**D) NaHCO3 - Sodium Bicarbonate**
Sodium bicarbonate (NaHCO3), commonly known as baking soda, decomposes when heated to form sodium carbonate (Na2CO3), water (H2O), and carbon dioxide (CO2). The reaction is as follows:
2 NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g)

Therefore, options A (Na2CO3), B (Li2CO3), and D (NaHCO3) form metal oxide on heating, while option C (K2SO4) forms potassium pyrosulfate instead.