Question

Lanthanoids are

• A. 14 elements in the seventh period (atomic no. = 90 to 103) that are filling 5f sublevel.
• B. 14 elements in the sixth period (atomic no. 58 to 71) that are filling 4f sublevel
• C. 14 elements in the seventh period (atomic no. = 58 to 71) that are filling 4f sublevel
• D. 14 elements in the sixth period (atomic no. 90 to 103) that are filling 4fsub level

Answer 1

The Correct Option is B

The question requires us to identify which set of elements are the lanthanoids based on their period, atomic numbers, and the sublevel that is being filled.

Let's address each option:

1. Option 1: "14 elements in the seventh period (atomic no. = 90 to 103) that are filling 5f sublevel."
   This describes actinides, not lanthanoids. Actinides are located in the seventh period and involve the filling of the 5f sublevel.

2. Option 2: "14 elements in the sixth period (atomic no. 58 to 71) that are filling 4f sublevel."
   This is the correct description of lanthanoids. Lanthanoids, also known as lanthanides, consist of elements with atomic numbers 58 to 71 and involve the filling of the 4f sublevel. These elements belong to the sixth period of the periodic table.

3. Option 3: "14 elements in the seventh period (atomic no. = 58 to 71) that are filling 4f sublevel."
   This option confuses the periods. The elements with atomic numbers 58 to 71 are part of the sixth period, filling the 4f sublevel, not the seventh period.

4. Option 4: "14 elements in the sixth period (atomic no. 90 to 103) that are filling 4f sublevel."
   The atomic numbers 90 to 103 refer to actinides, and they fill the 5f sublevel, not the 4f sublevel. Therefore, this is incorrect.

Therefore, among the options provided, the correct description for lanthanoids is the second option.

Correct Answer: 14 elements in the sixth period (atomic no. 58 to 71) that are filling 4f sublevel.