1) what is the atomic number of iron  a) 26 b) 22 c) 18 2) in which cycle the phosphorus element is located? a) 3 b) 1 c) 5 3) how many types of matter we have? a) 3 b) 4 c) 2 4) what is the gas that is present with the highest percentage in the air a) nitrogen b) oxygen c) hydrogen 5) what is the percentage of oxygen gas in the air? a) 21% b) 18% c) 30%

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