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
