Possible Clues:

• Laughing gas, familiarly
• Kind of acid
• Containing nitrogen, especially in a low valency state
• — oxide (anesthetic)
• -- oxide (laughing gas)
• Dentistry number, familiarly
• Laughing gas, for short
• No sweet tin is overturned in a chemical way
• ___ oxide (laughing gas)
• __ oxide: laughing gas