What is the half-life of an isotope that decays to 6.25% of its original activity in 18.9 hours?

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Find the mass in grams of 1.37x1020 particles of h3po4

For the reaction shown, calculate how many moles of no2 form when each of the following completely reacts. 2n2o5(g)→4no2(g)+o2(g) part a 1.0 mol n2o5 express your answer using two significant figures. nothing mol m o l request answer part b 5.4 mol n2o5 express your answer using two significant figures.