Exa-12.1(a)   
The following method of representing atoms is followed throughout the chapter
		 x,ySz
 where x=atomic number y=mass number z= Neutron Number S=symbol of the atom

The helium can be reperesented as 2,4He2
 
 Exa-12.1(b)   
The helium can be reperesented as 50,116Sn66
 
 Exa-12.1(c)   
The helium can be reperesented as 92,235U143