When polonium-210 emits am alpha particle, the child isotope has an atomic mass of?

Polonium-210 has a Atomic mass of 210 g/mol. The reaction of decay is shown as,
                        ²¹⁰₈₄Po > ᵇₐX + ⁴₂He
where,
                         X = Unknown Element
                          ᵇ = Atomic Mass of Unknown Element
                          ᵃ = Atomic number of Unknown Element
Solving for ᵇ,
                            210  =  ᵇ  +  4
                                 ᵇ  = 210 - 4
                                 ᵇ  = 206

Solving for ₐ ,
                            84  =  ₐ  +  2
                               ₐ  =  84 - 2
                               ₐ  =  82

Now, Putting values in ᵇ and ₐ of X,

                                                      ²⁰⁶₈₂X
Searching Periodic table for atomic number 82.

                                                       ²⁰⁶₈₂Pb

Result: The child Isotope is Lead (Pb) having atomic number 82 and Atomic mass 206 g/mol.

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