Which of the following compound is thermally most stable ?

Options

A. `LiNO_(3)`
B. `NaNO_(3)`
C. `KNO_(3)`
D. `RbNO_(3)`

Answer

To determine which of the given compounds is thermally most stable, we can follow these steps:

### Step 1: Identify the Compounds
The compounds given are:
- LiNO3 (Lithium Nitrate)
- NaNO3 (Sodium Nitrate)
- KNO3 (Potassium Nitrate)
- RbNO3 (Rubidium Nitrate)

### Step 2: Understand Thermal Stability
Thermal stability refers to the ability of a compound to resist decomposition when subjected to heat. In general, the thermal stability of alkali metal nitrates increases as we move down the group in the periodic table.

### Step 3: Analyze the Alkali Metals
The alkali metals in the order of increasing atomic number are:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)

As we move down this group, the size of the metal cation increases, which affects the thermal stability of the corresponding nitrate.

### Step 4: Apply the Trend
From the trend observed in alkali metal nitrates:
- LiNO3 is the least thermally stable.
- NaNO3 is more stable than LiNO3 but less stable than KNO3.
- KNO3 is more stable than both LiNO3 and NaNO3.
- RbNO3 is the most thermally stable among these nitrates.

### Step 5: Conclusion
Based on the trend that thermal stability increases down the group of alkali metals, we conclude that RbNO3 (Rubidium Nitrate) is the thermally most stable compound among the options provided.

### Final Answer
The compound that is thermally most stable is **RbNO3 (Rubidium Nitrate)**.

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