Question

Assertion (A): Ionization enthalpy increases along each series of transition elements from left to right. However, small variations occur. Reason (R): There is a corresponding increase in nuclear charge which accompanies the filling of electrons in the inner d-orbitals.

• A. (A) is correct but (R) is not correct
• B. (A) is not correct but (R) is correct
• C. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• D. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Hint:

\(d\)-electrons shield poorly compared to \(s\)- and \(p\)-electrons. Hence effective nuclear charge increases significantly across transition series.

Answer 1

The Correct Option is C

Concept: Ionization enthalpy is the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom. It mainly depends upon:
• Effective nuclear charge
• Atomic size
• Shielding effect
• Stability of electronic configuration

Step 1: Analyzing the Assertion.
Across the transition series, atomic number increases continuously. As protons increase, nuclear charge also increases. Electrons are added into inner \(d\)-orbitals, but \(d\)-electrons do not shield effectively. Therefore outer electrons experience stronger attraction from nucleus. Hence more energy is required to remove electrons. Thus ionization enthalpy generally increases from left to right. However, due to:
• half-filled stability
• fully-filled stability
• electron repulsion small irregular variations occur. Hence Assertion is true.

Step 2: Analyzing the Reason.
Reason states that nuclear charge increases while electrons are filled in inner \(d\)-orbitals. This statement is correct. Increase in nuclear charge causes stronger attraction on valence electrons. Hence ionization enthalpy increases.

Step 3: Checking the relationship between A and R.
The Reason directly explains why ionization enthalpy increases across transition series. Therefore: \[ \text{Both A and R are true and R correctly explains A.} \] Final Answer: \[ \boxed{\text{Both A and R are true and R correctly explains A}} \]