Question

Uranium-235 undergoes nuclear fission as shown in the diagram below.

A small gray ball labeled n impacts a large mass of red and gray balls labeled superscript 235 subscript 92 upper U. The impact gives off a smaller mass of balls labeled superscript 139 subscript 56 upper B a, a starburst labeled 200 megavolts, which in turn gives off 2 balls labeled n; and another smaller mass of balls labeled X.

Which element does X represent?
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Answer 1

X is krypton-95 (symbol 95/36 Kr).

Work: mass numbers: 236 (235U + n) = 139 + A_X + 2(1) → A_X = 95. Atomic numbers: 92 = 56 + Z_X → Z_X = 36 → element Kr. Equation: n + 235U → 139Ba + 95Kr + 2 n + ~200 MeV.