Chemistry 2002 JAMB Past Questions - Question 5: Which of the following gases contains the least number of atoms at s.t.p.?

Correct Answer

A

Explanation

To determine which gas contains the least number of atoms at standard temperature and pressure (STP), we need to consider Avogadro's Law. Avogadro's Law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

At STP (0 degrees Celsius or 273.15 Kelvin and 1 atmosphere pressure), one mole of any ideal gas occupies a volume of 22.4 liters.

Now, let's compare the number of atoms in one mole of different gases:

1. **Hydrogen (H2):** One mole of hydrogen gas (H2) contains 6.022 x 10^23 molecules. Each molecule of hydrogen consists of two atoms. So, one mole of hydrogen contains \( 6.022 \times 10^{23} \times 2 \) atoms.

2. **Oxygen (O2):** One mole of oxygen gas (O2) also contains 6.022 x 10^23 molecules. Each molecule of oxygen consists of two atoms. So, one mole of oxygen contains \( 6.022 \times 10^{23} \times 2 \) atoms.

3. **Nitrogen (N2):** Like oxygen and hydrogen, one mole of nitrogen gas (N2) contains 6.022 x 10^23 molecules. Each molecule of nitrogen consists of two atoms. So, one mole of nitrogen contains \( 6.022 \times 10^{23} \times 2 \) atoms.

Since all these gases contain the same number of atoms in one mole (Avogadro's number), they have an equal number of atoms at STP. The number of atoms is not determined by the type of gas but by Avogadro's number, which is a constant.