Which of the next represents the Avogadro number ?

Options

A. Number of molecules present in 1 L of gas at N.T.P.
B. Number of molecules present in 22.4 mL of gas at N.T.P.
C. Number of molecules present in 22.4 L of gas at 298 K and 1 atm. Pressure
D. Number of molecules present in one mole of gas at any temp, and pressure

Explanation

To determine which option represents Avogadro's number, we need to first understand what Avogadro's number is and how it relates to moles and particles.

### Step-by-Step Solution:

1. **Definition of Avogadro's Number**:
- Avogadro's number is defined as the number of particles (atoms, molecules, etc.) in one mole of a substance.
- It is approximately equal to \(6.022 \times 10^{23}\) particles.

2. **Understanding Moles**:
- One mole of any substance contains Avogadro's number of particles. This means that regardless of the type of gas or substance, one mole will always contain \(6.022 \times 10^{23}\) particles.

3. **Analyzing the Options**:
- **Option 1**: "Number of molecules present in one liter of gas at NTP" - This is incorrect because at Normal Temperature and Pressure (NTP), one mole of gas occupies 22.4 liters, not one liter.
- **Option 2**: "22.4 ml" - This is also incorrect. The volume of one mole of gas at NTP is 22.4 liters, not milliliters.
- **Option 3**: "22.4 liters" - While this is the correct volume for one mole of gas at NTP, it does not represent Avogadro's number directly.
- **Option 4**: "The number of molecules present in one mole of a gas at any temperature or pressure" - This is correct because it directly states that one mole contains Avogadro's number of molecules.

4. **Conclusion**:
- The correct answer is **Option 4**: "The number of molecules present in one mole of a gas at any temperature or pressure."