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NEET CHEMISTRYMedium

The number of unpaired electrons in a paramagnetic diatomic molecule of an element with atomic number 16 is:

A

2

B

3

C

4

D

1

Step-by-Step Solution

  1. Identify the Element: The element with atomic number 16 is Sulphur (S).
  2. Identify the Molecule: The question refers to its paramagnetic diatomic form, which is S2S_2 (typically found in the vapour phase at high temperatures).
  3. Determine Valence Electrons: Sulphur belongs to Group 16 (like Oxygen). Electronic configuration: [Ne]3s23p4[Ne] 3s^2 3p^4. Each sulphur atom contributes 6 valence electrons. Total valence electrons in S2=6+6=12S_2 = 6 + 6 = 12.
  4. Apply Molecular Orbital Theory (MOT): The filling order for valence electrons (analogous to O2O_2) is: σ3s2<σ3s2<σ3pz2<(π3px2=π3py2)<(π3px1=π3py1)\sigma_{3s}^2 < \sigma_{3s}^{*2} < \sigma_{3p_z}^2 < (\pi_{3p_x}^2 = \pi_{3p_y}^2) < (\pi_{3p_x}^{*1} = \pi_{3p_y}^{*1})
  5. Count Unpaired Electrons: The last 2 electrons occupy the two degenerate antibonding π\pi^* orbitals singly (following Hund's Rule). Thus, there are 2 unpaired electrons.

(Note: While the specific properties of S2S_2 are covered in the p-Block elements chapter, the principles of paramagnetism and unpaired electrons are detailed in the provided Class 12 Chemistry source, Unit 4 and 5, and the methodology derives from general Chemical Bonding.)

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