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Here is the link to a great video that explains your question nicely, hope this helps.
I believe it would be the first option. It forms iron oxide (rust) when exposed to moisture and air.
They are the outer layer of the electron layers.
Answer:
The Key difference between average vs weighted average is that simple average is nothing but simply adding up all the observation values and dividing the same by the total number of observations to calculate the average whereas weighted average is an average where each observation value will have a frequency assigned.
Explanation: