Question

The isotope silicon-32 decays into phosphorus-32. Silicon-32 has a half-life of 170 years and can be used to find the age of rocks it is contained in. Which two statements are true regarding this scenario? PICK TWO
A) Silicon-32 is the stable daughter isotope and phosphorous-32 is the unstable parent isotope.

B) In a given rock sample, the amount of silicon-32 isotope gets divided in half about every 170 years.

C) The half-life can be used to determine the amount of silicon-32 that has decayed from the time the closure temperature was reached.

D) In a given rock sample, as the amount of silicon-32 lessens, so does the amount of phosphorous-32.

E) In a given rock sample, the amount of silicon-32 is always equal to the amount of phosphorous-32.

Answer 1

The correct answers are B & C. Silicon-32 is the parent isotope, which decays into phosphorus-32 (daughter isotope). The silicon-32 amount is halved every 170 years, so we can use this to determine how old the rock is. The amount of phosphorus-32 increases over time, but it is not equal to the amount of silicon-32.