Question

If a big nucleus is hit by an energetic object (an alpha or a neutron, for example), the big nucleus often will break apart. Usually there will be 2 large pieces and a bunch of tiny pieces (like pottery hit by a baseball). Consider this reaction :
n + ²³⁹₉₄Pu → ( ^CA_CZCX ) → ¹²⁸₅₀Sn + ¹⁰²_ZX + ^____{___}α + N n .
What is the Z of the big nucleus (besides the tin, which is given!), and how many neutrons are there at the end (called "N" , in reaction above) ?

₄₀Zr ; 6 n

₄₀Zr ; 10 n

₃₆Kr ; 6 n

₄₆Pd ; 6 n

₄₆Pd ; 14 n

₄₂Mo ; 6 n

₄₄Ru ; 6 n

₄₄Ru ; 10 n

₄₂ Mo ; 8 n

Answer 1

n + ²³⁹₉₄Pu → ( ^CA_CZCX ) → ¹²⁸₅₀Sn + ¹⁰²_ZX + ^____{___}α + N n

we can write

¹₀ n + ²³⁹₉₄Pu → ¹²⁸₅₀Sn + ¹⁰²_ZX + ⁴₂α + N ¹₀n

total number of protons left side of the reaction = 0 + 94 = 94

total number of protons right hand side = 50 + z + 2 + 0 = 52 + z

from conservation of number pof protons

total number of protons right hand side = total number of protons left side

52 + z = 94

or, z = 94 - 52

or, z = 42

z = 42 corresponsd to Molybdenum (Mo)

total mass number left side of the erquation = 1 + 239 = 240

total mass number right side of the equation = 128 + 102 + 4 + (N x1) = 234 + N

from coservation of mass number

total mass number right side of the equation = total mass number left side of the erquation

234 + N = 240

or, N = 240 - 234

or, N = 6

hence, correct option is ₄₂Mo ; 6 n