Metal `M+"air" overset(delta)(to)Aoverset(H_(2)O)(to)Boverset(HCl)(to)` White fumes, Metal M can be:

Options

A. Li, Mg
B. Li, Al or K
C. Na, K or Mg
D. Li, Na or K

Answer

To solve the problem, we will analyze the reactions step by step to identify the metal M based on the given information.

### Step 1: Identify the final product from the reaction with HCl
- We know that when substance B reacts with HCl, it produces white fumes. The white fumes are typically associated with ammonium chloride (NH4Cl), which suggests that B is ammonia (NH3).

**Hint:** Consider common reactions that produce white fumes; ammonium chloride is a key indicator.

### Step 2: Determine what A must be
- Since we established that B is ammonia (NH3), we need to find out what A is. The problem states that A is formed when metal M reacts with water. The hydrolysis of a metallic nitrite (MNO2) produces ammonia. Therefore, A must be a metal nitrite.

**Hint:** Look for a metal that can form nitrites when reacting with water.

### Step 3: Identify the metal M
- Now we need to determine which metal can react with air to form a nitrite. Among the alkali metals, only lithium (Li) can react with nitrogen in the air to form lithium nitride (Li3N). Other alkali metals like sodium (Na) and potassium (K) do not form nitrides.

**Hint:** Recall the reactivity of alkali metals with nitrogen; only Li forms nitrides.

### Step 4: Confirm the options
- The options provided were:
- A: Li, Mg
- B: Li, Al
- C: Na, K
- D: Li, Na, K
- Since we have established that metal M must be either lithium or magnesium (as magnesium can also form nitrites), the correct option is A (Li, Mg).

**Hint:** Eliminate options based on the ability to form nitrides; focus on the reactivity of lithium and magnesium.

### Final Answer
The metal M can be **Li (Lithium)** or **Mg (Magnesium)**, but since only lithium is known to form nitrides with nitrogen in the air, the most suitable answer is **Li**.

### Summary of Steps:
1. Identify the product from HCl (white fumes = NH4Cl).
2. Determine that A must be a metal nitrite.
3. Identify that M must be a metal that can form nitrites (Li or Mg).
4. Confirm the options and select the correct one.