Argon is perticularly important for the metal industry, being used as an inert gas shield in arc
Weather satellites and Doppler radar, helps the process of looking over a large area, an does the network of weather observations.
The answer to your question is C
NaOH, is not an element, but a compund. Meaning it's chemically bonded. Na is sodium, O is oxygen and H is hydrogen.
Sodium is a metal, Oxygen is a non-metal and hydrogen is also not a metal.
Meaning that this is an Ionic compound. Hope this helps.