Question

Which of the following statements are correct?

1. The electronic configuration of Cr is [Ar] 3d⁵4s¹.
2. The magnetic quantum number may have a negative value.
3. In the ground state of an atom, the orbitals are filled in order of their increasing energies.
4. The total number of nodes are given by n – 2.

Choose the most appropriate answer from the options given below :

• A. (A), (C) and (D) only
• B. (A) and (B) only
• C. (A) and (C) only
• D. (A), (B) and (C) only

Answer 1

The Correct Option is D

Let's evaluate each statement one by one to determine which are correct.

1. The electronic configuration of Cr is [Ar] 3d⁵4s¹.
   Chromium (Cr) is an exception to the expected electron configuration due to its preference for half-filled subshell stability. Instead of [Ar] 3d⁴4s², it is actually [Ar] 3d⁵4s¹, as this configuration provides extra stability. Therefore, this statement is correct.
2. The magnetic quantum number may have a negative value.
   The magnetic quantum number (m_l) can indeed have negative values. For a given value of angular momentum quantum number (l), m_l can range from -l to +l, including zero. Hence, this statement is also correct.
3. In the ground state of an atom, the orbitals are filled in order of their increasing energies.
   According to the Aufbau principle, electrons fill orbitals starting with the lowest available energy states before filling higher ones, following the order of increasing energy. Thus, this statement is correct.
4. The total number of nodes are given by n – 2.
   The total number of nodes in an atomic orbital is given by n – 1, where n is the principal quantum number. Therefore, this statement is incorrect.

Based on the above explanations, the correct statements are (A), (B), and (C), confirming the provided correct answer: (A), (B) and (C) only.