Explanation:

Dalton's law of partial pressure states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of each individual gas. This law assumes that the gases behave ideally and do not interact with each other.

In the given options, the mixture of Cl₂ and SO₂ does not obey Dalton's law of partial pressure.

Reasoning:

When Cl₂ and SO₂ gases are mixed together, they can undergo a chemical reaction to form a new compound, sulfur dichloride (SCl₂). This reaction is highly exothermic and can occur even at room temperature.

Cl₂(g) + SO₂(g) -> SCl₂(g)

The formation of SCl₂ changes the composition of the mixture and therefore alters the partial pressures of Cl₂ and SO₂. As a result, the total pressure of the mixture will not be equal to the sum of the partial pressures of Cl₂ and SO₂, violating Dalton's law of partial pressure.

Therefore, the correct answer is option C, Cl₂ and SO₂.

Other options:

a) O₂ and CO₂: These gases do not undergo any chemical reaction with each other. They will behave as ideal gases and obey Dalton's law of partial pressure.

b) N₂ and O₂: Similarly, these gases do not react with each other and will obey Dalton's law of partial pressure.

d) CO₂ and He: CO₂ and He are also non-reacting gases, so they will follow Dalton's law of partial pressure.

In conclusion, the mixture of Cl₂ and SO₂ does not obey Dalton's law of partial pressure due to the possibility of a chemical reaction between the two gases.

C