Question

The statement that is not correct for periodic classification of elements is:

• A. The properties of elements are periodic function of their atomic numbers.
• B. Non-metallic elements are less in number than metallic elements.
• C. For transition elements, the \(3d\)-orbitals are filled with electrons after \(3p\)-orbitals and before \(4s\)-orbitals.
• D. The first ionisation enthalpies of elements generally increase with increase in atomic number as we go along a period.

Hint:

In the periodic table, the properties of elements are periodic functions of their atomic numbers. The order of filling orbitals for transition elements is \(4s\) before \(3d\), not the other way around.

Answer 1

The Correct Option is C

Step 1: Periodic Classification of Elements Explained
The periodic table's arrangement is based on the periodic law: element properties are periodic functions of their atomic numbers.
Step 2: Statement Analysis
Statement (A): Accurate. The periodic law confirms properties are periodic functions of atomic numbers.
Statement (B): Accurate. Metallic elements outnumber non-metallic elements.
Statement (C): Inaccurate. For transition elements, \(3d\) orbitals fill *after* \(4s\) orbitals, not before. The correct filling order is \(3p\), \(4s\), then \(3d\).
Statement (D): Accurate. First ionization enthalpies typically rise with increasing atomic number across a period.
Step 3: Identifying the Erroneous Statement
Statement (C) is incorrect due to its misrepresentation of orbital filling order in transition elements.Final Answer: Statement (C) is incorrect. It incorrectly states that for transition elements, \(3d\) orbitals fill after \(3p\) orbitals and before \(4s\) orbitals.