A nucleus ${}_Z{}^{A}X$ has mass represented by m(A, Z). If $m_p$ and $m_n$ denote the mass of proton and neutron respectively and BE is the binding energy (in MeV), then:

1. BE = [m(A, Z) - Z$m_p$- (A - Z)$m_n$] $c^2$

2. BE = [Z$m_p$+ (A - Z)$m_n$- m(A,Z)] $c^2$

3. BE = [Z$m_p$+ A$m_n$- m(A, Z)] $c^2$

4. BE = m(A, Z) - Z$m_p$- (A, Z)$m_n$

Half-lives of two radioactive substances A and B respectively are 20 min and 40 min.  Initially, the samples of A and B have an equal number of nuclei. After 80 min the ratio of the remaining number of A and B nuclei is:

1. 1 : 16

2. 4 : 1

3. 1 : 4 

4. 1 : 1

Radioactive ${}_{27}{}^{60}Co$ is transformed into stable ${}_{28}{}^{60}Ni$ by emitting two $\gamma$-rays of energies

1. 1.33 MeV and 1.17 MeV in succession

2. 1.17 MeV and 1.33 MeV in succession

3. 1.37 MeV and 1.13 MeV in succession

4. 1.17 MeV and 1.13 MeV in succession

The volume occupied by an atom is greater than the volume of the nucleus by factor of about

1. ${10}^{10}$ 

2. ${10}^{15}$ 

3. ${10}^1$ 

4. ${10}^5$

A radioactive nucleus undergoes a series of decay according to the scheme 
$A \xrightarrow{\alpha} A_1 \xrightarrow{\beta} A_2 \xrightarrow{\alpha} A_3 \xrightarrow{\gamma} A_4$

What fraction of a radioactive material will get disintegrated in a period of two half-lives?

1. whole

2. half

3. one-fourth

4. three-fourth

If the nucleus ${}_{13}{}^{27}Al$ has a nuclear radius of about 3.6 fm, then ${}_{52}{}^{125}Te$ would have its radius approximately as 

1. 6.0 fm 

2. 9.6 fm

3. 12.0 fm 

4. 4.8 fm

After two hours, one-sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is

1. 15 minutes 

2. 30 minutes

3. 45 minutes

4. 1 hour

Atomic weight of boron is 10.81 and it has two isotopes ${}_5{}^{10}B and {}_5{}^{11}B$. Then, the ratio of atoms of  ${}_5{}^{10}B and {}_5{}^{11}B$ in nature would be 

1. 19 : 81

2. 10 : 11 

3. 15 : 16 

4. 81 : 19