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

282.

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

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

A radioactive substance containing N atoms emits n $\alpha$ - particles per second. Half-life of the substance is :

• $\frac{\mathrm{N}}{\mathrm{n}}$ sec

• $\frac{\mathrm{n}}{\mathrm{N}}$ sec

• $\frac{0.693\mathrm{n}}{\mathrm{N}}$ sec

• $\frac{0.693\mathrm{N}}{\mathrm{n}}$ sec

In a radioactive decay,

           ₉₂U²³⁸ _{$\stackrel{\mathrm{\alpha }}{\to }$  X  $\stackrel{\mathrm{\alpha }}{\to }$  Z}Y^A

The values of Z and A

• 92 , 236

• 88 , 230

• 90 , 130

• 88 , 234

In a sample of radioactive substance, what percentage decays in one mean life time?

• 69.3 %

• 63 %

• 50 %

• 36 %

Number of nuclei of a radioactive substance at time t = O are 2000 and 1800 at time t = 2s. Number of nuclei left after t = 6s is

• 1442

• 1554

• 1652

• 1458

₉₂U²³⁸ on absorbing a neutron goes over to ₉₂U²³⁹. This nucleus emits an electron to go over to neptunium which on further emitting an electron goes over to plutonium. The resulting plutonium can be expressed as

• ₉₄Pu²³⁹

• ₉₀Pu²¹⁹

• ₉₃Pu²⁴⁰

• ₉₂Pu²⁴⁰

The radius of nucleus of silver (atomic number = 47) is 3.4 x 10^-14 m. The electric potential on the surface of nucleus is (e = 1.6 x 10^-19 C)

• 1.99 x 10⁶ V

• 2.9 x 10⁶ V

• 4.99 × 10⁶ V

• 0.99 x 10⁶ V