### Correct Option: C ### Detailed Explanation: When nitrates are heated, they undergo thermal decomposition, which means they break down into simpler substances. The behavior of different metal nitrates upon heating varies based on the metal involved. Let's analyze the nitrates of potassium (K), magnesium (Mg), and iron (Fe) to understand their decomposition products. 1. **Potassium Nitrate (KNO₃)**: - When heated, potassium nitrate decomposes to form potassium nitrite (KNO₂) and oxygen (O₂): \[ 2 KNO_3 (s) \rightarrow 2 KNO_2 (s) + O_2 (g) \] - This means potassium nitrate does not produce an oxide but rather a nitrite and oxygen. 2. **Magnesium Nitrate (Mg(NO₃)₂)**: - Magnesium nitrate decomposes upon heating to produce magnesium oxide (MgO), nitrogen dioxide (NO₂), and oxygen (O₂): \[ 2 Mg(NO_3)_2 (s) \rightarrow 2 MgO (s) + 4 NO_2 (g) + O_2 (g) \] - This indicates that magnesium nitrate does indeed produce an oxide, which is magnesium oxide. 3. **Iron(II) Nitrate (Fe(NO₃)₂)**: - Iron(II) nitrate decomposes similarly to magnesium nitrate, producing iron(II) oxide (FeO), nitrogen dioxide (NO₂), and oxygen (O₂): \[ 2 Fe(NO_3)_2 (s) \rightarrow 2 FeO (s) + 4 NO_2 (g) + O_2 (g) \] - This shows that iron nitrate also produces an oxide. 4. **Iron(III) Nitrate (Fe(NO₃)₃)**: - Iron(III) nitrate decomposes to iron(III) oxide (Fe₂O₃), nitrogen dioxide (NO₂), and oxygen (O₂): \[ 4 Fe(NO_3)_3 (s) \rightarrow 2 Fe_2O_3 (s) + 12 NO_2 (g) + O_2 (g) \] - This indicates that iron(III) nitrate also produces an oxide. ### Analysis of Options: - **Option A: All the nitrates decompose to their oxides.** - **Incorrect**: While magnesium and iron nitrates do produce oxides, potassium nitrate does not; it produces nitrite and oxygen instead. - **Option B: The nitrate of magnesium gives the nitrite and oxygen.** - **Incorrect**: Magnesium nitrate decomposes to magnesium oxide, nitrogen dioxide, and oxygen, not nitrite. - **Option C: The nitrates of magnesium and iron give the oxides.** - **Correct**: Both magnesium nitrate and iron nitrate decompose to produce their respective oxides (MgO and FeO/Fe₂O₃). - **Option D: The nitrate of iron gives the nitrite and oxygen.** - **Incorrect**: Iron nitrate decomposes to produce oxides, not nitrites. ### Summary of Key Points: - Potassium nitrate decomposes to form nitrite and oxygen, not an oxide. - Magnesium and iron nitrates decompose to produce their respective oxides. - The decomposition products vary significantly among different metal nitrates. - Understanding the specific decomposition reactions is crucial for predicting the products of thermal decomposition. ### Revision Summary: - Potassium nitrate → nitrite + oxygen (not an oxide). - Magnesium nitrate → magnesium oxide + nitrogen dioxide + oxygen. - Iron nitrate → iron oxide + nitrogen dioxide + oxygen. - Only magnesium and iron nitrates produce oxides upon heating.