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The half life of a radioactive isotope X is 50 years. It decays to another element Y
which is stable. The two elements X and Y were found to be in the ratio of 1: 15 in a
sample of a given rock. The age of the rock was estimated to be
  • a)
    100 years
  • b)
    150 years
  • c)
    200 years
  • d)
    250 years
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
The half life of a radioactive isotope X is 50 years. It decays to ano...
After t second fractional amount of X left is  
t = 4 × T1/2
t = 4 × 50
= 200 years
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Most Upvoted Answer
The half life of a radioactive isotope X is 50 years. It decays to ano...
X:y=1:15
initial value of X=N0
after decay the amount of X remain=No/16N=No(1/2)*t/T
No/16/No=(1/2)*t/50
1/16=(1/2)*t/50=(1/2)*4=(1/2)*t/50
4=t/50
t=200years
Free Test
Community Answer
The half life of a radioactive isotope X is 50 years. It decays to ano...
The half-life of a radioactive isotope is the time it takes for half of the initial amount of the isotope to decay. In this case, the half-life of isotope X is given as 50 years. This means that after 50 years, half of the isotope X will have decayed to form the stable element Y.

To determine the age of the rock, we can use the ratio of X to Y in the sample. The ratio is given as 1:15, which means that for every 1 unit of X, there are 15 units of Y.

Let's assume that the initial amount of X in the rock sample is 1 unit. After 50 years, half of this amount will have decayed, leaving 0.5 units of X. At the same time, Y would have been formed, so the total amount of Y in the sample would be 15 units.

After another 50 years (totaling 100 years), half of the remaining X will decay. This means that 0.25 units of X will be left. At the same time, the amount of Y will increase to 30 units.

We can continue this process, halving the amount of X every 50 years and doubling the amount of Y. After 150 years, there will be 0.125 units of X and 60 units of Y.

After 200 years, there will be 0.0625 units of X and 120 units of Y.

Finally, after 250 years, there will be 0.03125 units of X and 240 units of Y.

At this point, the ratio of X to Y is approximately 1:15, which matches the given ratio in the rock sample. Therefore, the age of the rock is estimated to be 200 years.

So, the correct answer is option C) 200 years.
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The half life of a radioactive isotope X is 50 years. It decays to another element Ywhich is stable. The two elements X and Y were found to be in the ratio of 1: 15 in asample of a given rock. The age of the rock was estimated to bea)100 yearsb)150 yearsc)200 yearsd)250 yearsCorrect answer is option 'C'. Can you explain this answer?
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