Assertion : The order of atomic radii of `Cu, Ag` and `Au` is `Cu lt Ag ~~ Au`.
Reason : The atomic radii of `4d` series elements are larger than those of `3d` series elements but generally the radii of `4d` and `5d` series elements are almost identical.

Options

A. Statement-1 is true , Statement-2 is true and Statement-2 is correct explanation for Statement-1
B. Statement-1 is true, Statement-2 is True and Statement-2 is Not correct explanation for statement-1
C. Statement-1 is true, Statement-2 is False
D. Statement-1 is False, Statement-2 is True

Explanation

To solve the assertion and reasoning question regarding the atomic radii of copper (Cu), silver (Ag), and gold (Au), we will analyze both the assertion and the reason step by step.

### Step 1: Analyze the Assertion
The assertion states that the order of atomic radii of Cu, Ag, and Au is Cu < Ag < Au.

- **Understanding Atomic Radii**: Atomic radius generally increases down a group in the periodic table due to the addition of electron shells. Therefore, we expect that as we move from Cu (3d series) to Ag (4d series) to Au (5d series), the atomic radius should increase.

- **Comparison**:
- Cu (atomic number 29) has a smaller atomic radius compared to Ag (atomic number 47) because Ag is in the next period and has an additional electron shell.
- Similarly, Au (atomic number 79) is larger than Ag due to being in the next period again.

- **Conclusion for Assertion**: The assertion is true: Cu < Ag < Au.

### Step 2: Analyze the Reason
The reason states that the atomic radii of 4d series elements are larger than those of 3d series elements, but generally, the radii of 4d and 5d series elements are almost identical.

- **Understanding the Reason**:
- It is a known fact that the atomic radii of 4d series elements (like Ag) are indeed larger than those of 3d series elements (like Cu) due to the addition of a new electron shell.
- However, the statement about the 4d and 5d series elements being almost identical in size is due to the phenomenon known as lanthanide contraction, which affects the size of the elements in these series.

- **Conclusion for Reason**: The reason is true, but it does not correctly explain the assertion about the order of atomic radii. The assertion is based on the general trend of atomic sizes, while the reason discusses a specific comparison that is not directly related to the assertion.

### Final Conclusion
- The assertion is true.
- The reason is true but does not serve as a correct explanation for the assertion.

### Answer:
The correct option is that the assertion is true, the reason is true, but the reason is not the correct explanation of the assertion.

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