Which of the following statement is correct about oxidation number ?

Options

A. Oxidation number of all atoms in elementary state is zero
B. The sum of Oxidation number of all the atoms in the formula of a compound is always zero
C. Alkali and alkaline earth metals have +1 and +2 oxidation staes respectively
D. All of these

Answer

To determine which statement about oxidation numbers is correct, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** The oxidation number of all atoms in their elemental state is 0.

**Explanation:**
- In their elemental form, elements exist as single atoms or molecules (e.g., O2, N2, Fe, etc.). The oxidation number for any atom in its elemental state is always 0 because there are no charges present.
- For example, in O2, each oxygen atom has an oxidation number of 0.

**Conclusion:** This statement is correct.

### Step 2: Analyze the second statement
**Statement:** The sum of oxidation numbers of all atoms in a formula of a compound is always 0.

**Explanation:**
- In a neutral compound, the sum of the oxidation numbers of all the atoms must equal 0.
- For example, in HNO3:
- Hydrogen (H) has an oxidation number of +1.
- Nitrogen (N) has an oxidation number of +5.
- Oxygen (O) has an oxidation number of -2 (there are three oxygen atoms, contributing -6).
- The total is: +1 (H) + 5 (N) - 6 (O) = 0.

**Conclusion:** This statement is also correct.

### Step 3: Analyze the third statement
**Statement:** Alkali and alkaline earth metals have +1 and +2 oxidation states respectively.

**Explanation:**
- Alkali metals (Group 1) such as lithium (Li) and sodium (Na) have one electron in their outermost shell, which they lose to achieve a stable electronic configuration, resulting in a +1 oxidation state.
- Alkaline earth metals (Group 2) such as beryllium (Be) and magnesium (Mg) have two electrons in their outermost shell, which they lose to achieve stability, resulting in a +2 oxidation state.

**Conclusion:** This statement is correct as well.

### Final Conclusion
Since all three statements are correct, the correct answer to the question is "All of these."