‹ Back to the paper
A plant or any other living being maintains a reasonable balance of C-14 (radioactive carbon) in…
A plant or any other living being maintains a reasonable balance of C-14 (radioactive carbon) in its tissue during its lifetime. C-14 is used to determine the age of fossils. In the upper atmosphere, neutrons present in the cosmic rays are captured to produce the following nuclear reaction.
$_7\text{N}^{14} + {}_0\text{n}^1 \longrightarrow {}_6\text{C}^{14} + {}_1\text{H}^1$
C-14 isotope is circulated in the atmosphere and gets absorbed by living organism during photosynthesis. The ratio of C-14 to C-12 in living being is $1:10^{12}$. Once the living being dies, the level of C-14 in the dead being decreases due to the following reaction.
$_6\text{C}^{14} \longrightarrow {}_7\text{N}^{14} + {}_{-1}\text{e}^0 + \gamma\text{ rays}$
The death of the plant brings an end to its tendency to take up C-14. The half-life period of C-14 is 5770 years. By knowing the concentration of C-14 in the living plant and the piece of dead material at a particular time, the age of the material (fossil) can be determined.
Read the passage carefully and answer the questions that follow.
(i)[1.0]
Write the relation between the decay constant and half-life period.
(ii)[1.0]
In a piece of dead wood, the activity or concentration of C-14 is found to be one third of its initial activity. Calculate the age of the old wood.
(iii)[1.0]
The half-life period ($t_{1/2}$) for a first order reaction is 30 minutes. Calculate the time taken to complete $87\cdot5\%$ of the reaction.
Answer
No answer yet.
From ISC 2025 Specimen Chemistry Paper 1, question 1(C).