Under similar conditions of P and T, equal volume of all gases contains equal number of molecules. It is

Options

A. Boyle's law
B. Charles' law
C. Gay Lussac's
D. Avogadro's law

Explanation

To solve the question "Under similar conditions of P and T, equal volume of all gases contains equal number of molecules," we need to identify the law that describes this phenomenon.

### Step-by-Step Solution:

1. **Understand the Question**: The question states that under the same pressure (P) and temperature (T), equal volumes of different gases contain the same number of molecules. This is a fundamental concept in gas laws.

2. **Identify the Relevant Law**: The law that describes this relationship is known as **Avogadro's Law**. Avogadro's Law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules.

3. **Use the Ideal Gas Equation**: The ideal gas equation is given by:
\[ PV = nRT \]
where:
- \( P \) = pressure
- \( V \) = volume
- \( n \) = number of moles
- \( R \) = universal gas constant
- \( T \) = temperature

4. **Analyze the Equation**: If pressure (P) and temperature (T) are constant, then \( R \) is also constant. This means that the product \( PV \) is directly proportional to the number of moles (n):
\[ V \propto n \]
Therefore, if the volume (V) is the same for different gases, the number of moles (n) must also be the same.

5. **Conclusion**: Since the number of moles is directly related to the number of molecules (1 mole contains \( 6.022 \times 10^{23} \) molecules), it follows that equal volumes of all gases at the same temperature and pressure contain an equal number of molecules. Thus, the statement in the question is a reflection of Avogadro's Law.

### Final Answer:
The statement is a reflection of **Avogadro's Law**.

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