Answer: a) Thorium
b) 

Step-by-step explanation:
Alpha decay : When a larger nuclei decays into smaller nuclei by releasing alpha particle. In this process, the mass number and atomic number is reduced by 4 and 2 units respectively. 
General representation of an element is given as: 
 
 
where, 
Z represents Atomic number 
A represents Mass number 
X represents the symbol of an element 
General representation of alpha decay : 
 
 

Hence the name of the product nuclide is Thorium and the symbol for the product nuclide is 
