Question

Which of the following oxides is paramagnetic?

• A. SO$_2$
• B. NO$_2$
• C. SiO$_2$
• D. CO$_2$

Hint:

Using a simple frame or just bolding for the box Key Points: Paramagnetic substances have unpaired electrons and are attracted to magnetic fields. Diamagnetic substances have all electrons paired and are weakly repelled by magnetic fields. Molecules with an odd total number of valence electrons are typically paramagnetic. Molecules with an even total number of valence electrons are typically diamagnetic (important exception: O$_2$).

Answer 1

The Correct Option is B

Paramagnetism results from unpaired electrons within a molecule or ion. Substances with unpaired electrons are drawn to an external magnetic field. Diamagnetic substances, possessing only paired electrons, are weakly repelled by a magnetic field.\r\n\r\nA simplified method for predicting paramagnetism in simple molecules involves counting valence electrons. An odd total indicates at least one unpaired electron, signifying paramagnetism. An even total usually implies diamagnetism, although exceptions like O₂ exist, necessitating Molecular Orbital Theory for explanation.\r\n\r\nLet's calculate total valence electrons for each oxide:\r\n

\r\n
• (A) SO₂: Sulfur (Group 16) has 6 valence electrons. Oxygen (Group 16) has 6 valence electrons.
  Total = 6 + 2(6) = 18 electrons (Even). Expected to be diamagnetic.
\r\n
• (B) NO₂: Nitrogen (Group 15) has 5 valence electrons. Oxygen (Group 16) has 6 valence electrons.
  Total = 5 + 2(6) = 17 electrons (Odd). Expected to be paramagnetic.
\r\n
• (C) SiO₂: Silicon (Group 14) has 4 valence electrons. Oxygen (Group 16) has 6 valence electrons.
  Total = 4 + 2(6) = 16 electrons (Even). Expected to be diamagnetic. (Note: SiO₂ is a network solid, but the fundamental bonding involves paired electrons).
\r\n
• (D) CO₂: Carbon (Group 14) has 4 valence electrons. Oxygen (Group 16) has 6 valence electrons.
  Total = 4 + 2(6) = 16 electrons (Even). Expected to be diamagnetic.
\r\n

\r\nSince NO₂ has an odd number of total valence electrons (17), it must contain at least one unpaired electron, thus exhibiting paramagnetism. The other oxides, with even valence electron counts, are diamagnetic.\r\n\r\n