Question

$someone \: explain \: this \: question \\ and \: answer.$
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Answer 1

in question we have to calculate mass of 2.5g oxygen atom not oxygen molecule so mass of oxygen we know 16g...

according to question..

moles =given mass /molar mass..

so, given mass =2.5g. and atomic mass =16g..

putting value. 2.5×16=40..

hope it helps you..
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by - - AKSHITA