Thallium-207 has a half-life of 4.77 minutes. If an initial sample weighed 155 grams, and now only weighs 2.42 grams, how many half-lives have occurred?
A.4
B.6
C.5
D.3

Answer(false);

Ithink that one is (c)

Answer is: value of q is 5·10⁻⁶m.chemical reaction: mg²⁺(aq) + co₃²⁻(aq) → mgco₃(s).c(mg²⁺) = 2.5·10⁻³ m; concentration of magnesium cations.c(co₃²⁻) = 2.00·10⁻³ m; concentration of carbonate anions.q = c(mg²⁺)  · c(co₃²⁻).q = 2.5·10⁻³ m  · 2.00·10⁻³ m.q = 5·10⁻⁶m.q = 0.000005 m.