Which one of the following statements is correct ?

Options

A. All elements are heterogenous in nature
B. Compounds made up of a number of elements are heterogenous
C. A mixture is always heterogenous
D. Air is a homogenous mixture

Answer

To determine which statement is correct among the given options, we need to analyze each statement carefully.

### Step-by-Step Solution:

1. **Evaluate the First Statement: "All elements are heterogeneous in nature."**
- Elements are pure substances that consist of only one type of atom. They do not have a varied composition; hence, they are not heterogeneous. This statement is **incorrect**.

2. **Evaluate the Second Statement: "Compounds made up of a number of elements are heterogeneous."**
- Compounds consist of elements that are chemically combined in a fixed ratio. This means they have a uniform composition throughout. Therefore, compounds are **not** heterogeneous. This statement is **incorrect**.

3. **Evaluate the Third Statement: "A mixture is always heterogeneous."**
- Mixtures can be either homogeneous or heterogeneous. For example, a solution of salt in water is a homogeneous mixture, while a mixture of sand and salt is heterogeneous. Thus, this statement is **incorrect**.

4. **Evaluate the Fourth Statement: "Air is a homogeneous mixture."**
- Air is a mixture of gases (mainly nitrogen, oxygen, and small amounts of other gases) that are uniformly distributed. You cannot distinguish the individual components easily, which makes air a homogeneous mixture. This statement is **correct**.

### Conclusion:
The correct statement is: **"Air is a homogeneous mixture."**