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 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

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 $\frac{{\mathrm{\lambda }}_1}{{\mathrm{\lambda }}_2}$ is

• m₁/m₂

• m₂/m₁

• 1.0

• $\sqrt{\frac{{\mathrm{m}}_2}{{\mathrm{m}}_1}}$

Which of the following nuclei is fissionable but not possible?

• ${}_{92}\mathrm{U}^{235}$

• ${}_{92}\mathrm{U}^{233}$

• ${}_{92}\mathrm{U}^{238}$

• ${}_{94}\mathrm{Pu}^{239}$

In nuclear reaction

${}_{72}{}^{180}\mathrm{X} \stackrel{-\mathrm{\alpha }}{\to } \mathrm{Y} \stackrel{-\mathrm{\beta }}{\to } \mathrm{Z} \stackrel{-\mathrm{\alpha }}{\to } \mathrm{A} \stackrel{-\mathrm{\gamma }}{\to } \mathrm{P}$

the atomic mass and number of P are, respectively:

• 170,69

• 172,69

• 172,70

• 170,70

A radioactive substance has activity 64 times higher than the required normal level. If T_1/2 = 2h, then the time, after which it should be possible to work with it, is:

• 16 h

• 6 h

• 10 h

• 12 h

In a mean life of radioactive sample :

• about $\frac{1}{3}$ of substance disintegrates

• about  $\frac{2}{3}$ of substance disintegrates

• about 90% of the substance disintegrates

• almost all the substance disintegrates

If the half-life of any sample of a radioactive substance is 4 days, then the fraction of the sample will remain undecayed after 2 days, will be

• $\sqrt{2}$

• $\frac{1}{\sqrt{2}}$

• $\frac{\sqrt{2} - 1}{\sqrt{2}}$

• $\frac{1}{2}$

For the stability of any nucleus:

• binding energy per nucleon will be more

• binding energy per nucleon will be less

• no. of electrons will be more

• none of these

160.

Nuclear fusion is common to the pairs :

• thermonuclear reactor, uranium based nuclear reactor

• energy production in sun, uranium-based nuclear reactor

• energy production in sun, hydrogen bomb

• the disintegration of heavy nuclei, hydrogen bomb