Easy MCQ +4 / -1 PYQ · JEE Mains 2025

Consider the ground state of chromium atom $(Z=24)$. How many electrons are with Azimuthal quantum number $l=1$ and $l=2$ respectively ?

  1. A 16 and 5
  2. B 12 and 5 Correct answer
  3. C 12 and 4
  4. D 16 and 4

Solution

<p>The ground state electron configuration of chromium (Cr, $ Z = 24 $) is:</p> <p>$\text{Cr: } [\text{Ar}]\,3d^5\,4s^1$</p> <p>Let's break down the configuration:</p> <p>The noble gas core $[\text{Ar}]$ represents:</p> <p><p>$1s^2$ (with $l=0$)</p></p> <p><p>$2s^2$ (with $l=0$)</p></p> <p><p>$2p^6$ (with $l=1$)</p></p> <p><p>$3s^2$ (with $l=0$)</p></p> <p><p>$3p^6$ (with $l=1$)</p></p> <p>Electrons with azimuthal quantum number $l = 1$ are found in $p$ orbitals:</p> <p><p>$2p^6$: 6 electrons</p></p> <p><p>$3p^6$: 6 electrons</p></p> <p><p>Total $p$-electrons: $6 + 6 = 12$.</p></p> <p>Electrons with azimuthal quantum number $l = 2$ are found in $d$ orbitals:</p> <p>$3d^5$: 5 electrons</p> <p>Thus, there are 12 electrons with $l = 1$ and 5 electrons with $l = 2$.</p> <p>The correct option is Option B.</p>

About this question

Subject: Chemistry · Chapter: Atomic Structure · Topic: Bohr's Model

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