In the following questions a statement of assertion (A) is followed by a statement of reason ( R)
A : Lanthanum ( Z: 57) is lanthanoid .
R : Valence electrons are present in 4 f orbital.

Options

A. If Both Assertion & Reason are true and the reason is the correct explanation of the assertion then mark (1) .
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion then mark (2)
C. If Assertion is true statement but Reason is false then mark (3)
D. If both Assertion and Reason are false statements then mark (4)

Answer

To solve the given question, we need to evaluate both the assertion (A) and the reason (R) provided.

### Step 1: Analyze the Assertion (A)
**Assertion (A):** Lanthanum (Z: 57) is a lanthanoid.

- **Explanation:** Lanthanum has an atomic number of 57. It is often included in the lanthanoid series, which consists of elements with atomic numbers from 57 (Lanthanum) to 71 (Lutetium). However, it is important to note that Lanthanum is technically not a lanthanoid in the strict sense, as it does not have electrons filling the 4f subshell. Instead, its electronic configuration ends with 5d1, making it a d-block element.

### Step 2: Analyze the Reason (R)
**Reason (R):** Valence electrons are present in the 4f orbital.

- **Explanation:** The statement claims that the valence electrons of lanthanum are in the 4f orbital. However, for lanthanum, the valence electron is actually in the 5d orbital (5d1). The 4f orbital starts filling with the subsequent elements in the lanthanoid series (starting from Cerium, Z: 58). Therefore, this statement is incorrect.

### Conclusion
- **Assertion (A)** is **false** because Lanthanum is not a lanthanoid in the strict sense.
- **Reason (R)** is **false** because the valence electron of Lanthanum is in the 5d orbital, not the 4f orbital.

### Final Answer
Both the assertion and the reason are false.