Which of the following is/are correct ? I when heated , potassium nitrate does not decompose , but copper (II) nitrate decomposes readily II calcium hydroxide decomposes when heated to form calcium oxide and steam III magnesium carbonate decomposes more readily than zinc carbonate when both are heated . AII only BI and II only CI and III only DI , II and III only

To determine which of the statements are correct, let's analyze each one step by step:

Statement I: "When heated, potassium nitrate does not decompose." This statement is incorrect. When heated, potassium nitrate (KNO3) decomposes into potassium nitrite (KNO2) and oxygen gas (O2).

Statement II: "Copper (II) nitrate decomposes readily." This statement is correct. Copper (II) nitrate (Cu(NO3)2) decomposes when heated, producing nitrogen dioxide gas (NO2), oxygen gas (O2), and copper (II) oxide (CuO).

Statement III: "Magnesium carbonate decomposes more readily than zinc carbonate when both are heated." This statement is incorrect. Zinc carbonate (ZnCO3) decomposes more readily than magnesium carbonate (MgCO3) when heated. Zinc carbonate decomposes into zinc oxide (ZnO) and carbon dioxide gas (CO2), while magnesium carbonate decomposes into magnesium oxide (MgO) and carbon dioxide gas (CO2).

Based on the analysis, we can conclude that Statement II is correct, while Statements I and III are incorrect. Therefore, the correct answer is option B: "I and II only."