Which of the following statements are correct?
(A) The electronic configuration of Cr is [Ar] 3d⁵ 4s¹.
(B) The magnetic quantum number may have a negative value.
(C) In the ground state of an atom, the orbitals are filled in order of their increasing energies.
(D) The total number of nodes are given by n - 2.
Choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 5 steps

Test each statement on its own, and watch D: total nodes are n-1, not n-2.

1. Statement A. A half-filled 3d subshell is extra stable, so one 4s electron moves into 3d. Chromium is [Ar] 3d⁵ 4s¹, so A is correct.
2. Statement B. mₗ runs from -l to +l through zero. For a p orbital it can be -1, so B is correct.
3. Statement C. This is the Aufbau principle: in the ground state, electrons fill orbitals of lower energy first. C is correct.

   total nodes = n - 1 = l_(angular) + (n - l - 1)_(radial)

4. Statement D. The total is n-1, not n-2. A 1s orbital has 1-1 = 0 nodes, but n-2 would give -1, which is impossible. D is wrong.
5. So. A, B and C are correct and D is not, which is option (d).

The idea to keep. Radial nodes are n-l-1, angular nodes are l, and together they make n-1. Check any node formula on 1s: it must give zero.

Answer from the NTA final answer key. Solution by PrepWiser.