Answer : Option 1) nuclei of  and nuclei of
 and nuclei of  only.
 only.
Explanation : Radiation is spontaneously emitted from nuclei of  because this isotope of hydrogen is highly radioactive as compared to other isotopes of hydrogen namely; nuclei of
 because this isotope of hydrogen is highly radioactive as compared to other isotopes of hydrogen namely; nuclei of  and nuclei of
 and nuclei of  .
. 
They have much stable nucleus as compared to nuclei of  .
.
The more it is unstable the more radiations will be emitted from its nucleus.
 
        
                    
             
        
        
        
The formula of Density is known as:
Density = mass/volume
Units: g/cm^3
Hope this helps!