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? Superscript 95 Subscript 36 Baseline Upper K r Superscript 96 Subscript 36 Baseline Upper K r Superscript 97 Subscript 36 Baseline Upper K r Superscript 98 Subscript 36 Baseline Upper K r