Which of the following statements is/are true for all the alkali metals ?

Options

A. Their nitrates decompose on heating to give `NO_(2) and O_(2)`.
B. Their corbonates decompose on heatig to give `CO_(2)` and metal oxide.
C. They react with oxygen to give mainly the oxide `MO_(2)`
D. They react with halogens to give halides `M^(+)X^(-)`.

Answer

To determine which statements are true for all alkali metals, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Their nitrates decompose on heating to give NO2 and O2.**
- **Analysis:** When alkali metal nitrates are heated, they typically decompose to form nitrites and oxygen. However, lithium nitrate is an exception, as it decomposes to form lithium oxide, nitrogen dioxide, and oxygen. Therefore, this statement is not true for all alkali metals.
- **Conclusion:** **False**

2. **Statement 2: Their carbonates decompose on heating to give CO2 and metal oxide.**
- **Analysis:** All alkali metal carbonates decompose upon heating to produce carbon dioxide (CO2) and the corresponding metal oxide. For example, sodium carbonate decomposes to yield sodium oxide and carbon dioxide. This is a characteristic behavior of all alkali metal carbonates.
- **Conclusion:** **True**

3. **Statement 3: They react with oxygen to give mainly the oxide MO2.**
- **Analysis:** Alkali metals react with oxygen to form oxides, but the correct formula for the oxides formed is M2O, not MO2. The alkali metals form M+ cations, and oxygen forms O2- anions, leading to the formula M2O. Therefore, this statement is incorrect for all alkali metals.
- **Conclusion:** **False**

4. **Statement 4: They react with halogens to give halides M+X-.**
- **Analysis:** Alkali metals react with halogens to form halides, and the resulting compounds are indeed of the form M+X-. For example, sodium reacts with chlorine to form sodium chloride (NaCl). This is a general property of alkali metals.
- **Conclusion:** **True**

### Final Summary:
- **True Statements:**
- Statement 2: Their carbonates decompose on heating to give CO2 and metal oxide.
- Statement 4: They react with halogens to give halides M+X-.

- **False Statements:**
- Statement 1: Their nitrates decompose on heating to give NO2 and O2.
- Statement 3: They react with oxygen to give mainly the oxide MO2.