Which of the following molecules obeys the octet rule for all its atoms?

• A. ${\mathrm{CO}}_2$ (carbon dioxide)
• B. ${\mathrm{PCl}}_5$ (phosphorus pentachloride)
• C. ${\mathrm{BF}}_3$ (boron trifluoride)
• D. ${\mathrm{NO}}_2$ (nitrogen dioxide)

Answer: (A)

Verified step by step guidance

1. Identify the central atom and the total number of valence electrons for each molecule to determine their Lewis structures.
2. Draw the Lewis structure for carbon dioxide (CO\_2) and check if all atoms have eight electrons around them, satisfying the octet rule.
3. Draw the Lewis structure for phosphorus pentachloride (PCl\_5) and note that phosphorus can have an expanded octet because it is in period 3, so it may not obey the octet rule strictly.
4. Draw the Lewis structure for boron trifluoride (BF\_3) and observe that boron often has an incomplete octet with only six electrons, so it does not obey the octet rule for all atoms.
5. Draw the Lewis structure for nitrogen dioxide (NO\_2) and recognize that it is a radical with an odd number of electrons, so not all atoms will have a complete octet.