1. Answer is ₉₂²³⁵U
Since this is an alpha emission the atomic number
of the daughter nucleus decreases by 2 while mass number decreases by 4 compared to
parent atom. Since parent atom has 94 as atomic number the daughter atom should
have 94 - 2 = 92 as atomic number and 239 - 4 = 235 as mass
number.
₉₄²³⁹Pu → ₂⁴He + ₉₂²³⁵U
2. Answer is ₉₁²³⁴Pa
Since this is a beta emission, a neutron is
converted into a proton while emitting an electron. Hence atomic number
increases by 1 compared to mass number but mass number remains as same. Hence,
the atomic number of the
daughter atom should be 90 + 1 = 91 which belongs to Pa. But the mass number is same
as 234.
₉₀²³⁴Th → ₋₁⁰e + ₉₁²³⁴Pa
3. Answer is ₈¹⁸O
Since this is a positron emission, a proton is converted into a neutron
while emitting an positron. Hence atomic number decreases by 1 compared to mass
number but mass number remains as same. Hence, the atomic number of the
daughter atom should be 9- 1
= 8 which belong to O. But the mass
number is same as 18.
₉¹⁸F → ₊₁⁰e + ₈¹⁸O
4. Answer is ₈₀²⁰¹Hg
This is an electron capture
decay. A proton is converted into a neutron by emitting
a gamma ray. In this process mass number remains
as same as parent atom which is 201, but the atomic number is
decreased by 1 than parent atom. Hence atomic number of
daughter nucleus is 81 -1 = 80 which belongs to Hg.
₈₁²⁰¹Tl + ₋₁⁰e → ₀⁰γ + ₈₀²⁰¹Hg
