Which of the following statement is/are correct?
(i) An element of a substance contains only one kind of atoms.
(ii) In CO2, carbon and oxygen chemically combined in a fixed proportion of 3 : 8 by mass.
(iii) The constituents of the pure substances can be separated by simple physical methods.
(iv) Milk is a homogeneous mixture.

Options

A. (i) and (ii)
B. (i) , (iii) and (iv)
C. Only (i)
D. (i) , (ii) , (iii) and (iv)

Answer

To determine which of the statements are correct, let's analyze each one step by step.

### Step 1: Analyze Statement (i)
**Statement (i):** An element of a substance contains only one kind of atoms.

**Analysis:**
- An element is defined as a pure substance that cannot be broken down into simpler substances by chemical means.
- Elements consist of only one type of atom. For example, carbon (C) consists only of carbon atoms, and oxygen (O) consists only of oxygen atoms.

**Conclusion:** This statement is **correct**.

### Step 2: Analyze Statement (ii)
**Statement (ii):** In CO2, carbon and oxygen chemically combined in a fixed proportion of 3:8 by mass.

**Analysis:**
- The molecular formula for carbon dioxide (CO2) indicates that one carbon atom combines with two oxygen atoms.
- The atomic mass of carbon (C) is approximately 12 g/mol, and the atomic mass of oxygen (O) is approximately 16 g/mol.
- Therefore, the mass of carbon in CO2 is 12 g, and the mass of oxygen is 2 × 16 g = 32 g.
- The ratio of the mass of carbon to the mass of oxygen is 12:32, which simplifies to 3:8.

**Conclusion:** This statement is **correct**.

### Step 3: Analyze Statement (iii)
**Statement (iii):** The constituents of the pure substances can be separated by simple physical methods.

**Analysis:**
- Pure substances, such as elements and compounds, cannot be separated into their components by physical methods.
- For example, diamond (a form of carbon) cannot be separated into carbon atoms using physical methods because the atoms are chemically bonded together.

**Conclusion:** This statement is **incorrect**.

### Step 4: Analyze Statement (iv)
**Statement (iv):** Milk is a homogeneous mixture.

**Analysis:**
- Milk is actually a heterogeneous mixture because it contains fat globules and other components that do not uniformly mix.
- When left to stand, the fat rises to the top, indicating that it is not homogeneous.

**Conclusion:** This statement is **incorrect**.

### Final Conclusion:
The correct statements are:
- Statement (i) is correct.
- Statement (ii) is correct.
- Statements (iii) and (iv) are incorrect.

Thus, the correct answer is that statements (i) and (ii) are correct.

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