$^{200}X \,:\, 90\%$ $^{199}X\, :\, 8.0\%$ $^{202}X\, :\, 2.0\%$
Weight of \(^{199} X=0.08 \times 199=15.92 u\)
Weight of \(^{202} X=0.02 \times 202=4.04 u\)
Total weight \(=199.96 \approx 200 u\)
$I.\,SeO_3^{2 - } + BrO_3^ - + {H^ + } \to SeO_4^{2 - } + B{r_2} + {H_2}O$
$II.\,BrO_3^ - + AsO_2^ - + {H_2}O \to B{r^ - } + AsO_4^{3 - } + {H^ + }$