Equal volumes of all gases under similar conditions of temperature and pressure contain equal number of atoms.

Answer

To solve the question regarding the statement that "equal volumes of all gases under similar conditions of temperature and pressure contain equal number of atoms," we can break it down step by step.

### Step-by-Step Solution:

1. **Understanding the Statement**: The statement refers to a principle in chemistry that relates to gases. It suggests that when gases are measured under the same conditions of temperature and pressure, they will have the same number of particles (atoms or molecules) in equal volumes.

2. **Berzelius Hypothesis**: This principle is attributed to the scientist Jöns Jacob Berzelius and is known as the Berzelius hypothesis. It states that at standard temperature and pressure (STP), which is defined as 0 degrees Celsius (273.15 K) and 1 atmosphere of pressure, equal volumes of all gases contain an equal number of particles.

3. **Avogadro's Law**: The concept is closely related to Avogadro's Law, which states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This means that one mole of any gas occupies the same volume at STP.

4. **Volume of One Mole of Gas**: At STP, one mole of any ideal gas occupies a volume of 22.4 liters. This means that regardless of the type of gas, if you have 22.4 liters of it at STP, it contains one mole of gas.

5. **Avogadro's Number**: One mole of any substance contains Avogadro's number of particles, which is approximately \(6.022 \times 10^{23}\) particles (atoms or molecules). Therefore, 22.4 liters of any gas at STP contains \(6.022 \times 10^{23}\) particles.

6. **Conclusion**: Thus, the statement that "equal volumes of all gases under similar conditions of temperature and pressure contain equal number of atoms" is validated by the principles of the Berzelius hypothesis and Avogadro's Law. At STP, equal volumes of gases indeed contain the same number of atoms or molecules.