Q31 / 180 · COMEDK 2025 (25 May Shift) · Chemistry
The pair of molecules that contain odd electron molecule and expanded octet.
- A$\mathrm{SF}_6, \mathrm{PCl}_5$
- B$\mathrm{BF}_3, \mathrm{SF} 6$
- Correct answerC$\mathrm{NO}_2, \mathrm{PCl}_5$
- D$\mathrm{NO}, \mathrm{AlCl}_3$
Solution
An odd electron molecule is one that contains an unpaired electron in its valence shell. Among the given options, $\mathrm{NO}_2$ has a total of $5 + 6 \times 2 = 17$ valence electrons, which is an odd number, making it an odd electron molecule.
An expanded octet molecule is one where the central atom has more than 8 electrons in its valence shell. In $\mathrm{PCl}_5$, the central phosphorus atom is bonded to five chlorine atoms, resulting in $5 \times 2 = 10$ electrons in its valence shell, which exceeds the octet rule.
Checking other options:
$\mathrm{SF}_6$ has an expanded octet (12 electrons), but $\mathrm{PCl}_5$ also has an expanded octet, not an odd electron molecule.
$\mathrm{BF}_3$ is an electron-deficient molecule (incomplete octet).
$\mathrm{NO}$ is an odd electron molecule, but $\mathrm{AlCl}_3$ is an electron-deficient molecule (incomplete octet).
Therefore, the pair containing an odd electron molecule and an expanded octet is $\mathrm{NO}_2$ and $\mathrm{PCl}_5$.
Answer: $\mathrm{NO}_2, \mathrm{PCl}_5$
An expanded octet molecule is one where the central atom has more than 8 electrons in its valence shell. In $\mathrm{PCl}_5$, the central phosphorus atom is bonded to five chlorine atoms, resulting in $5 \times 2 = 10$ electrons in its valence shell, which exceeds the octet rule.
Checking other options:
$\mathrm{SF}_6$ has an expanded octet (12 electrons), but $\mathrm{PCl}_5$ also has an expanded octet, not an odd electron molecule.
$\mathrm{BF}_3$ is an electron-deficient molecule (incomplete octet).
$\mathrm{NO}$ is an odd electron molecule, but $\mathrm{AlCl}_3$ is an electron-deficient molecule (incomplete octet).
Therefore, the pair containing an odd electron molecule and an expanded octet is $\mathrm{NO}_2$ and $\mathrm{PCl}_5$.
Answer: $\mathrm{NO}_2, \mathrm{PCl}_5$
Hence, the correct answer is option: 'C'.