Strontium-90 is a radioactive material that decays according to the function \( A(t)=A_{0} e^{-0.0244 t} \), where \( A_{0} \) is the inifial amount present and \( A \) is the amount present at time \( t \) (in years). Assume that a scientist has a sample of 800 grams of strontium- 90 . (a) What is the decay rate of strontium- 90 ? (b) How much strontium- 90 is left after 40 years? (c) When will only 200 grams of strontium- 90 be left? (d) What is the halt-life of strontium- 90 ?

Balancea por óxido - reducción las ecuaciones siguientes: \( \begin{array}{l}\text { 1) } \mathrm{HNO}_{3}+\mathrm{S} \\ \begin{array}{l}\text { Semireacción de oxidación } \\ \text { Agente oxidante } \longrightarrow\end{array} \\ \mathrm{NO}_{2}+\end{array} \mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O} \) \( \begin{array}{l}\text { Semireacción de reducción } \\ \text { Agente reductos }\end{array} \)

4. \( \mathrm{H}-\mathrm{CH} * \mathrm{O} \) 5. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CO}-\mathrm{CH}_{3} \) 6. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{O}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3} \) 7. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{NH}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3} \) 8. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} \) 9. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH} * \mathrm{O} \) 10. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}-\mathrm{F} \) 11. \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3} \)

Son los coeficientes de la ecuación al balancerala por el método redox \( \mathrm{KMnO}_{4}+\mathrm{Zn}+\mathrm{H}_{2} \mathrm{SO}_{4} \xrightarrow{\mathrm{KHSO}_{4}+\mathrm{MnSO}_{4}+\mathrm{ZnSO}_{4}+\mathrm{H}_{2} \mathrm{O}} \) \( \begin{array}{llll}\text { a) } 2,5,9,2,2,5,8 & \text { b) } 8,2,5,9,2,2,5 & \text { c) } 5,8,2,5,8,2,2 & \text { d) } 2,5,8,2,5,8,2\end{array} \)

If the half-life of I-131 is 7.4 days, how many days would it take for only \( 3.2 \times \) \( 10^{-2} \) grams of \( 1-131 \) to be left in Mr. Miller's body if Dr. Goodie started him on an initial dose of 5.5 grams?

Types of Chemical Reactions \( \quad \) Which of the following is only produced by a double