The half-life of radium-226 is 1590 years. (a) A sample of radium-226 has a mass of 50 mg. Find a formula for the mass of the sample that remains after t years. (b) Find the mass after 500 years correct to the nearest milligram. (c) When will the mass be reduced to 40 mg

Explanation:

a )

m = m₀

m is mass after time t . original mass is m₀ , λ is disintegration constant

λ = .693 / half life

= .693 / 1590

= .0004358

m = m₀

b )

m = 50 x

= 40.21 mg .

c )

40 = 50

.8 =

= 1.25

.0004358 t = .22314

t = 512 years .

i think   the answer is c hope i'm right

fe 55.85 g/mol and h2o 18.02 g/mol.