Answer: -
When bismuth-212 undergoes alpha decay, it becomes ²⁰⁸Tl
Explanation: -
Mass number of ²¹²Bi = 212
Atomic number of ²¹²Bi = 83
When alpha decay occurs the mass number decreases by 4 and the atomic number decreases by 2.
Mass number of daughter = 212 - 4 = 208
Atomic number of daughter = 83 - 2 = 81
It is the atomic number of Thallium Tl.
Thus the daughter nucleide is ²⁰⁸Tl.
Can you take picture of the whole question? I can’t see.
The largest atomic radius has Ba,because they are all metals of 2nd group,but as you know when you go down upright in the periodic table the metallic features getting stronger but also orbital layers increasing,and you can say more layers larger atomic radius.Hope I helped,sorry for English
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