Question

The following represents a sequence of radioactive decays involving two α-particles and one
β-particle.
217At 85 V W X
α α β
What is the nuclide X?
A At 213
85 B r
215
77
I C Pb 209
82 D Tl

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Answer 1

Option (C) 209 Pb 82
Because after two alpha decay the mass will decrease by 8(217-8=209) and atomic number will decrease by 4(85-4=81). And after 1 beta decay,though it depends which type of beta decay it is but bu the options we can decide about it. And in this it is -ve Beta decay. So atomic number increases by 1 and there is no change in mass. So atomic number after beta decay is 82. Hence option (C) is correct.