Thallium-208 has a half-life of 3 minutes. How long will it take 60.0 g of thallium-208 to decay so that 15.0 g of the thallium-208 remains?
O3 min
O 6 min
O 9 min
O 11min Please explain how you got the answer?

The decay takes 6min

Explanation:

The decay of an isotope as Thallium-208 follows the equation:

ln[A] = -kt + ln[A]₀

Where [A] is amount of isotope after time t

k is decay constant = ln 2 / t(1/2)

[A]₀ is initial amount of the isotope

Replacing:

[A] = 15.0g

k = ln 2 / t(1/2) = ln 2 / 3min = 0.23105 min⁻¹

t = ?

[A]₀ = 60.0g

ln[A] = -kt + ln[A]₀

ln[15.0g] = -0.23105 min⁻¹*t + ln[60.0g]

-1.38629 = -0.23105 min⁻¹*t

6min = t

the answer is the

it's c. elements are placed in rows based on how may valencies electrons have.