Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Why are the noble gases found as single atoms, and not as molecules? Why is argon used inside filament bulbs instead of air? Why do airships use helium and not hydrogen, though hydrogen is lighter?
Group 1 metals are soft, have one outer electron and react with water to give hydrogen and an alkali; reactivity rises down the group. Group 2 metals are harder and less reactive. Halogens, group 17, get darker and less reactive down the group, and a more reactive halogen displaces a less reactive one. Noble gases have full shells.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Single atoms. Their outer shells are full, so the atoms do not bond, even to each other.
Step 2. Bulbs. Oxygen in air would burn the hot filament. Argon does not react with it.
Step 3. Airships. Hydrogen burns, and can explode. Helium is light and does not burn.
Answer: full shells; argon does not react with the filament; helium does not burn.
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