Question

Which of the following belongs to the d-block elements?

• A. Sodium
• B. Calcium
• C. Iron
• D. Helium

Hint:

d-block elements, also known as transition metals, lie in the middle of the periodic table in Groups 3 to 12.
Familiarity with the first transition series (Scandium to Zinc, \(Z = 21\) to \(30\)) is extremely important for competitive exams.
Iron (\(Fe\), \(Z=26\)) is a well-known member of this transition series.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify which of the listed chemical elements belongs to the d-block of the periodic table.

Step 2: Key Formula or Approach:
An element belongs to a particular block (s, p, d, f) depending on the subshell into which the last differentiating electron enters.

Step 3: Detailed Explanation:

• Electronic Configuration of Sodium: Sodium (\(Na\), \(Z = 11\)) has the electronic configuration:
  \[ 1s^2 2s^2 2p^6 3s^1 \]
  The last electron enters the \(3s\) orbital, making it an s-block element.
  
• Electronic Configuration of Calcium: Calcium (\(Ca\), \(Z = 20\)) has the electronic configuration:
  \[ 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 \]
  The last electron enters the \(4s\) orbital, making it an s-block element.
  
• Electronic Configuration of Iron: Iron (\(Fe\), \(Z = 26\)) has the electronic configuration:
  \[ 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2 \]
  The last electron enters the \(3d\) subshell, which classifies it as a d-block transition metal.
  
• Electronic Configuration of Helium: Helium (\(He\), \(Z = 2\)) has the electronic configuration:
  \[ 1s^2 \]
  Its valence shell is \(1s\), classifying it as an s-block element, though it is placed in Group 18 due to its noble gas properties.
  

Step 4: Final Answer:
Thus, Iron is the d-block element, which matches option (C).