## Chemistry and Chemical Reactivity (9th Edition)

$13.83\%$
Number of moles of the red solid: $0.206\ g\div288.915\ g/mol=0.000713\ mol$ From stoichiometry, that's the same number of moles of nickel (II) nitrate and NiS $0.000713\ mol\times 90.758\ g/mol=0.0647\ g$ Mass fraction: $0.0647\ g/0.468\ g\times100\%=13.83\%$