A : in third energy level there is no -f- subshell .
R : For n=3 the possible values of l are 0,1,2 and for f- subshell l = 3. .

Options

A. IF both assertion & reason are true and the reason is the correct explanation of the assertion then mark
B. IF both assertion & reason are true but the reason is not the correct explanation of the assertion , then mark
C. IF assertion is true statement but reason is false , then mark
D. If both assertion and reason are false statements then mark

Answer

To solve the question regarding the assertion and reason about the f subshell in the third energy level, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Quantum Numbers**:
- The principal quantum number (n) indicates the energy level of an electron in an atom. It can take positive integer values starting from 1 (n = 1, 2, 3, ...).
- The azimuthal quantum number (l) defines the shape of the orbital and can take values from 0 to (n-1).

2. **Identifying Values for n = 3**:
- For the third energy level (n = 3), the possible values of l are calculated as follows:
- l can take values: 0, 1, 2 (since l ranges from 0 to n-1).
- Therefore, for n = 3, the values of l are:
- l = 0 (s subshell)
- l = 1 (p subshell)
- l = 2 (d subshell)

3. **Determining the Absence of the f Subshell**:
- The f subshell corresponds to l = 3.
- Since for n = 3, the maximum value of l is 2, there is no possibility of having an f subshell in this energy level.

4. **Conclusion**:
- The assertion states that there is no f subshell in the third energy level, which is true.
- The reason given states that for n = 3, the possible values of l are 0, 1, and 2, and that l = 3 is required for an f subshell, which is also true.
- Therefore, both the assertion and reason are correct, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation of the assertion.

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