Answer:
a) 39/19 K : stable nuclide, 40/19 K : radioactive nuclide.
b) 209B: stable nuclide, 208Bi : radioactive nuclide
c) nickel-58 : stable nuclide, nickel-65 : radioactive nuclide.
Explanation:
As per the rule, nuclides having odd number of neutrons are generally not stable and therefore, are radioactive.
Mass number (A) = Atomic number (Z) + No. of neutrons (N)
Or, N = A - Z
a)
39/19 K and 40/19 K
Calculate no. of neutrons in 39/19 K as follows:
atomic no. = 19, mass no. 39
N = 39 - 19
= 20 (even no.)
Calculate no. of neutrons in 40/19 K as follows:
atomic no. = 19, mass no. 40
N = 40 - 19
= 21 (odd no.)
Therefore, 39/19 K is a stable nuclide and 40/19 K is a radioactive
nuclide.
b)
209Bi and 208Bi
Calculate no. of neutrons in 209Bi as follows:
atomic no. = 83, mass no. 209
N = 209 - 83
= 126 (even no.)
Calculate no. of neutrons in 208Bi as follows:
atomic no. = 83, mass no. 208
N = 208 - 83
= 125 (odd no.)
Therefore, 209Bi is a stable nuclide and 208Bi is a radioactive nuclide.
c)
nickel-58 and nickel-65
Calculate no. of neutrons in nickel-58 as follows:
atomic no. = 28, mass no. 58
N = 58 - 28
= 30 (even no.)
Calculate no. of neutrons in nickel as follows:
atomic no. = 28, mass no. 65
N = 65 - 28
= 37 (odd no.)
Therefore,nickel-58 is a stable nuclide and nickel-65 is a radioactive nuclide.
