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: Understanding the Periodic Classification of Elements
The periodic table is arranged based on the periodic law, which states that the properties of elements are a periodic function of their atomic numbers.
Step 2: Analyzing Each Statement
Statement (A) This is correct. The periodic law states that the properties of elements are periodic functions of their atomic numbers.
Statement (B): This is correct. Non
metallic elements are fewer in number compared to metallic elements.
Statement (C): This is incorrect. For transition elements, the \(3d\)
orbitals are filled after the \(4s\)
orbitals, not before. The correct order is \(3p\), \(4s\), and then \(3d\).
Statement (D): This is correct. The first ionisation enthalpies generally increase with increasing atomic number across a period.
Step 3: Identifying the Incorrect Statement
The incorrect statement is (C), as it misrepresents the order of filling of orbitals in transition elements. Final Answer: The incorrect statement is (C) For transition elements, the \(3d\)
orbitals are filled with electrons after \(3p\)
orbitals and before \(4s\)
orbitals.