35.5г

m(P2O5)=0,25*142=35,5г

дано

n(P2O5) = 0.25 mol

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m(P2O5)-?

M(P2O5) = 142 g/mol

m(P2O5) = n(P2O5)*M(P2O5) = 0.25 * 142 = 35.5 g

ответ 35.5 г