Question 7

Determine which molecules follow the Octet Rule (8 electrons in the valence shell of non-hydrogen atoms, 2 for hydrogen):

• $CO_2$: Carbon and Oxygen both complete their octets through double bonds. (Follows)
• $C_2H_4$: Both Carbons complete their octets through double and single bonds. (Follows)
• $HCl$: Chlorine completes its octet; Hydrogen follows the duet rule. (Follows)
• $O_3$: All oxygen atoms in ozone structures follow the octet rule. (Follows)
• $NO$: It is an odd-electron molecule (15 valence electrons). Nitrogen cannot satisfy the octet rule. (Doesn't follow)
• $NO_2$: It is an odd-electron molecule (17 valence electrons). (Doesn't follow)
• $BCl_3$: Boron has only 6 electrons in its valence shell (hypovalent). (Doesn't follow)
• $H_2SO_4$: Sulfur has 12 electrons in its valence shell (expanded octet/hypervalent). (Doesn't follow)

Analyzing options: (A) $CO_2$ (Yes), $C_2H_4$ (Yes), $NO$ (No), $HCl$ (Yes). Count = 3 molecules. Correct. (B) $NO_2$ (No), $O_3$ (Yes), $HCl$ (Yes), $H_2SO_4$ (No). Count = 2 molecules. Incorrect. (C) $BCl_3$ (No), $NO$ (No), $NO_2$ (No), $H_2SO_4$ (No). Count = 0 molecules. Incorrect. (D) $CO_2$ (Yes), $BCl_3$ (No), $O_3$ (Yes), $C_2H_4$ (Yes). Count = 3 molecules. Correct.