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JEE Advanced 2006
Exam
JEE Advanced
Year
2006
Subject
Chemistry
Chapter
Chemical Kinetics

JEE Advanced 2006 · Chemistry · Chemical Kinetics

Paragraph: Carbon-14 is used to determine the age of organic...

Paragraph: Carbon-14 is used to determine the age of organic material. The procedure is based on the formation of 14C{ }^{14} \mathrm{C} by neutron capture in the upper atmosphere. { }_7^{14} \mathrm{~N}+{ }_0^1 n \longrightarrow{ }_6^{14} \mathrm{C}+{ }_1 n¹ 14C{ }^{14} \mathrm{C} is absorbed by living organisms during photosynthesis. The 14C{ }^{14} \mathrm{C} content is constant in living organism once the plant or animal dies, the uptake of carbon dioxide by it ceases and the level of 14C{ }^{14} \mathrm{C} in the dead being, falls to the decay which 14C{ }^{14} \mathrm{C} undergoes. { }_6^{14} \mathrm{C} \longrightarrow{ }_7^{14}  N+β−\mathrm{~N}+\beta^{-}The half life period of 14C{ }^{14} \mathrm{C} is 5770 years. The decay constant (λ)(\lambda) can be calculated by using the following formula λ=0.693t1/2\lambda=\frac{0.693}{t_{1/2}}. The comparison of the β−\beta^{-}activity of the dead matter with that of the carbon still in circulation enables measurement of the period of the isolation of the material from the living cycle. The method however, ceases to be accurate over periods longer than 30,000 years. The proportion of 14C{ }^{14} \mathrm{C} to 12C{ }^{12} \mathrm{C} in living matter is 1:10121: 10^{12}.Question: Which of the following option is correct?

Options

  1. AIn living organisms, circulation of 14C{ }^{14} \mathrm{C} from atmosphere is high so the carbon content is constant in organism.
  2. BCarbon dating can be used to find out the age of earth crust and rocks.
  3. CRadioactive absorption due to cosmic radiation is equal to the rate of radioactive decay, hence the carbon content remains constant in living organisms.
  4. DCarbon dating can not be used to determine concentration of 14C{ }^{14} \mathrm{C} in dead beings.

Correct answer

C. Radioactive absorption due to cosmic radiation is equal to the rate of radioactive decay, hence the carbon content remains constant in living organisms.

Step-by-step solution

Radioactive absorption due to cosmic radiation is equal to the rate of radioactive decay, hence the carbon content as the ratio of C14\mathrm{C}^{14} to C12\mathrm{C}^{12} remains constant in living organism.
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