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Standard XII

Chemistry

Reaction Quotient

The number of...

Question

The number of U $^{238}$ nuclei in a rock sample is equal to the number of Pb $^{206}$ atoms. The half-life of U $^{238}$ is 4.5 x $10^{9}$ years.The age of the rock is

4.5 x10

^{9} y

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9x10

^{9} y

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13.5x10

^{9} y

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18x10

^{9} y

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Solution

The correct option is A 4.5 x10 $^{9} y$
As, $U^{238}$ disintegrates to form $P b^{206}$ atoms, the ratio of $U^{238} : P b^{206}$ is $1 : 1$ , i.e., 1 half life has been over as half of $U^{238}$ has decayed to form same amount of $P b^{206} .$

Thus the age of rock is 1 half life i.e., $4.5 \times 10^{9} y e a r s$

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Similar questions

Q. In a sample of rock, the ratio of

^{206} P b

^{238} U

nuclei is found to be 0.5. The age of the rock is (given half-life of

U^{238}

4.5 \times 10^{9}

years)

Q. A sample of rock from South America contains equal number of atoms of

U^{238}

and

P b^{206}

. The age of the rock will be :

^{238} U

decays with a half-life of

4.5 \times 10^{9}

years, the decay series eventually ending at

^{206} P b

, which is stable. A rock sample analysis shows that the ratio of the number of atoms of

^{206} P b

^{238} U

0.0058

. Assuming that all the

^{206} P b

is produced by the decay of

^{238} U

and that all other half-lives on the chain are negligible, the age of the rock sample is

(l n 1.0058 = 5.78 \times 10^{- 3})

Q. The weight based ratio of

U^{238}

and

P b^{226}

in a sample of rock in

4 : 3

. If the half life of

U^{238}

4.5 \times 10^{9}

years then the age of rock is

The weight based ratio of $U^{238}$ and $P b^{226}$ in a sample of rock is 4 : 3. If the half life of $U^{238}$ is $4.5 \times 10^{9}$ years, then the age of rock is:

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The number of U238 nuclei in a rock sample is equal to the number of Pb206 atoms. The half-life of U238 is 4.5 x 109 years.The age of the rock is

The correct option is A 4.5 x109yAs, U238 disintegrates to form Pb206 atoms, the ratio of U238:Pb206 is 1:1, i.e., 1 half life has been over as half of U238 has decayed to form same amount of Pb206.Thus the age of rock is 1 half life i.e., 4.5×109years

The number of U $^{238}$ nuclei in a rock sample is equal to the number of Pb $^{206}$ atoms. The half-life of U $^{238}$ is 4.5 x $10^{9}$ years.The age of the rock is