Elements A & B donot form solid bicarbonae but reacts with `N_2` to give nitrides. which f the following can be A & B?

Options

A. Li,Mg
B. Rb,Na
C. Ca,Cs
D. Ca,Na

Answer

To solve the problem, we need to identify elements A and B based on the following criteria:

1. **Do not form solid bicarbonates**: This means that the elements should not produce stable solid bicarbonate compounds.
2. **React with nitrogen to form nitrides**: This indicates that the elements can combine with nitrogen to create nitride compounds.

### Step-by-Step Solution:

**Step 1: Identify the elements that do not form solid bicarbonates.**
- Among the alkali metals, lithium is known to form a bicarbonate in solution, while sodium, potassium, rubidium, and cesium form solid bicarbonates. Therefore, we can conclude that element A must be lithium.

**Step 2: Check the reactivity of lithium with nitrogen.**
- Lithium reacts with nitrogen to form lithium nitride (Li3N), which is a stable compound. This satisfies the condition of forming nitrides.

**Step 3: Identify another element that does not form solid bicarbonates and can react with nitrogen.**
- Magnesium is known to react with nitrogen to form magnesium nitride (Mg3N2). Additionally, magnesium does not form solid bicarbonates like the other alkaline earth metals.

**Step 4: Confirm that magnesium and lithium meet both criteria.**
- Both lithium and magnesium do not form solid bicarbonates. Lithium forms a bicarbonate solution, while magnesium does not form stable solid bicarbonates. Both elements react with nitrogen to form stable nitrides (Li3N for lithium and Mg3N2 for magnesium).

**Conclusion:**
- The elements A and B that meet the criteria are lithium (Li) and magnesium (Mg).

### Final Answer:
Elements A and B are **Lithium (Li)** and **Magnesium (Mg)**.

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