A radioactive substance contains 10000 nuclei and its half-life p

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 Multiple Choice QuestionsMultiple Choice Questions

271.

A certain radioactive element has a half-life of 20 years. If we have a block with 10 g of the element in it, after how many years will there be just 2.5 g of the element in the block?

  • 80 years

  • 40 years

  • 100 years

  • 60 years


272.

The activity of a radioactive sample decreases to
(1/3)rd of its original value in 3 days. Then, in 9 days its activity will become

  • (1/27) of the original value

  • (1/9) of the original value

  • (1/18) of the original value

  • (1/3) of the original value


273.

If r1 and r2  are the radii of the atomic nuclei of mass numbers 64 and 125 respectively, then the ratio (r1/r2) is

  • 64/125

  • 64125

  • 5/4

  • 4/5


274.

A radioactive element forms its own isotope after 3 consecutive disintegrations. The particles emitted are

  • 3 β-particles

  • 2 β-particles and 1α-particle

  • 2 -βparticles and 1 γ-particle

  • 2 α-particles and 1 β-particle


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275.

A radioactive substance contains 10000 nuclei and its half-life period is 20 days. The number of nuclei present at the end of 10 days is

  • 7070

  • 9000

  • 8000

  • 7500


A.

7070

t = nT1/2

10 = n × 20

n = 1/2

we know,

NN0 = 12nN10000 = 121/2N = 100002 = 100001.414 = 7070


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276.

A radioisotope has a half-life of 5 yr. The fraction of the atoms of this material that would decay in 15 yr will be

  • 1

  • 2/3

  • 7/8

  • 5/8


277.

A particle of mass m at rest decays into two particles of masses m1 and m2 having non zero velocities. The ratio of de-Broglie wavelengths of the particles λ1λ2 is

  • m1/m2

  • m2/m1

  • 1.0

  • m2m1


278.

Which of the following nuclei is fissionable but not possible?

  • U23592

  • U23392

  • U23892

  • Pu23994


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279.

In nuclear reaction

X72180 -α Y -β Z -α A -γ P

the atomic mass and number of P are, respectively:

  • 170,69

  • 172,69

  • 172,70

  • 170,70


280.

A radioactive substance has activity 64 times higher than the required normal level. If T1/2 = 2h, then the time, after which it should be possible to work with it, is:

  • 16 h

  • 6 h

  • 10 h

  • 12 h


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