The correct answer is option 2: NaO. Sodium oxide is used as an anesthetic in medical procedures.
Option 1: N2, nitrogen gas, is not used as an anesthetic. It is a common atmospheric gas that does not have anesthetic properties.
Option 3: CH4, methane gas, is also not used as an anesthetic. It is primarily used as a fuel source and has no anesthetic effects.
Option 4: COa, which is not commonly used or known, is not used as an anesthetic. It is not a recognized compound and does not have any known anesthetic properties.
Therefore, the correct answer is option 2: NaO, as sodium oxide is commonly used as an anesthetic in medical procedures.