If M is the atomic mass and A is the mass number, packing fraction is given by:
(1) $\frac{\mathrm{A}}{\mathrm{M}-\mathrm{A}}$           

(2) $\frac{\mathrm{A}-\mathrm{M}}{\mathrm{A}}$
(3)$\frac{M}{\mathrm{M}-\mathrm{A}}$            

(4) $\frac{\mathrm{M}-\mathrm{A}}{\mathrm{A}}$

${\mathrm{M}}_{\mathrm{p}}$ denotes the mass of a proton and ${\mathrm{M}}_{\mathrm{n}}$ that of a neutron. A given nucleus of binding energy B contains Z protons and N neutrons. The mass M(N, Z) of the nucleus is given by:    (c is the velocity of light) 

(1) $\mathrm{M}(\mathrm{N}, \mathrm{Z})={\mathrm{NM}}_{\mathrm{n}}+{\mathrm{ZM}}_{\mathrm{p}}-{\mathrm{Bc}}^2$

(2) $\mathrm{M}(\mathrm{N}, \mathrm{Z})={\mathrm{NM}}_{\mathrm{n}}+{\mathrm{ZM}}_{\mathrm{p}}+{\mathrm{Bc}}^2$

(3) $\mathrm{M}(\mathrm{N}, \mathrm{Z})={\mathrm{NM}}_{\mathrm{n}}+{\mathrm{ZM}}_{\mathrm{p}}-\mathrm{B}/{\mathrm{c}}^2$

(4) $\mathrm{M}(\mathrm{N}, \mathrm{Z})={\mathrm{NM}}_{\mathrm{n}}+{\mathrm{ZM}}_{\mathrm{p}}+\mathrm{B}/{\mathrm{c}}^2$

Complete the reaction
$\mathrm{n}+{}_{92}{}^{235}\mathrm{U}\to {}_{56}{}^{144}\mathrm{Ba}+...+3\mathrm{n}$

1. ${}_{36}{}^{89}\mathrm{Kr}$      

2. ${}_{36}{}^{90}\mathrm{Kr}$

3. ${}_{36}{}^{91}\mathrm{Kr}$       

4. ${}_{36}{}^{92}\mathrm{Kr}$

1 atomic mass unit is equal to 
(1) $\frac{1}{25}$ (mass of ${\mathrm{F}}_2$ molecules)
(2) $\frac{1}{14}$ (mass of ${\mathrm{N}}_2$ molecules)
(3) $\frac{1}{12}$ (mass of one C-atom)
(4) $\frac{1}{16}$ (mass of ${\mathrm{O}}_2$ molecules)

The nucleus ${}_{92}{}^{234}\mathrm{U}$ splits exactly in half in a fission reaction in which two neutrons are released. The resultant nuclei are

(1) ${}_{46}{}^{116}\mathrm{Pd}$        

(2) ${}_{45}{}^{117}\mathrm{Rh}$

(3) ${}_{45}{}^{116}\mathrm{Rh}$       

(4) ${}_{46}{}^{117}\mathrm{Pd}$

A nucleus is bombarded with a high speed neutron so that resulting nucleus is a radioactive one. This phenomenon is called 

(1) Artificial radioactivity         

(2) Fusion

(3) Fission                               

(4) Radioactivity

Which of the following cannot cause fission in a heavy nucleus 

(1) $\mathrm{\alpha }$-particle         

(2) Proton

(3) Deutron             

(4) Laser rays

 If the mass number of an atom is A = 40 and its electron configuration is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^6$, the number of neutrons and protons in its nucleus will be 

(1) 22, 18           

(2) 18, 22

(3) 20, 20           

(4) 18, 18

Which of the following is most unstable

(1) Electrons           

(2) Protons

(3) Neutrons           

(4) $\mathrm{\alpha }$-particle

 Radioactive substance do not emit

(1) Electron           

(2) Helium nucleus

(3) Positron         

(4) Proton