Question

The mass of the radioactive isotope sodium-24 in a sample is initially measured at 7 milligrams. If the mass of the sodium-24 decreases by 25% every 12 hours, which of the following is closest to the mass of the sodium-24 in the sample 8 hours after the initial measurement?

Answer 1

The mass of sodium-24 at 8 hours after the initial experiment will be 3.5mg

The initial mass of the sodium-24 in a sample is = 7mg

It is given that every 12 hours 25% of mass decrease, that is,

                 12 hours = 25% of mass decreases

Lets find out 25% of mass which is  = (25/100)*7mg

                                                               = 0.25*7mg

                                                               = 1.75 mg

Now after 12 hours the mass will be = 7-1.75mg

                                                                 = 5.25 mg

Now we have to find the mass of the sodium-24 in 8 hours after the initial measurement.

Here we will apply unitary method,

According to the question,

                       12 hours =  5.25 mg

                        1 hours = 5.25/12 mg = 0.4375 mg

                        8 hours = 0.4375*8 mg

                                      = 3.5 mg

Hence the mass of sodium-24 at 8 hours after the initial experiment will be 3.5mg

Learn more about unitary method here : https://brainly.com/question/24587372

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