Em tham khảo nha:
\(\begin{array}{l}
3)\\
\% Fe\,trong\,FeO = \dfrac{{56}}{{56 + 16}} \times 100\% = 77,78\% \\
\% Fe\,trong\,F{e_2}{O_3} = \dfrac{{56 \times 2}}{{56 \times 2 + 16 \times 3}} \times 100\% = 70\% \\
\% Fe\,trong\,Fe{(OH)_3} = \dfrac{{56}}{{56 + 16 \times 3 + 1 \times 3}} \times 100\% = 52,34\% \\
\% Fe\,trong\,FeC{l_2} = \dfrac{{56}}{{56 + 35,5 \times 2}} \times 100\% = 44,09\% \\
\% Fe\,trong\,FeS{O_4}.5{H_2}O = \dfrac{{56}}{{56 + 32 + 16 \times 4 + 18 \times 5}} \times 100\% = 23,14\% \\
\Rightarrow \text{ Chất có nồng độ Fe cao nhất là FeO } \\
4)\\
\% {m_N}trong\,N{H_4}Cl = \dfrac{{14}}{{14 + 4 + 35,5}} \times 100\% = 26,17\% \\
\% {m_N}trong\,{(N{H_4})_2}S{O_4} = \dfrac{{14 \times 2}}{{14 \times 2 + 4 \times 2 + 32 + 16 \times 4}} \times 100\% = 21,21\% \\
\% {m_N}trong\,KN{O_3} = \dfrac{{14}}{{39 + 14 + 16 \times 3}} \times 100\% = 13,86\% \\
\% {m_N}trong\,{(N{H_2})_2}CO = \dfrac{{14 \times 2}}{{14 \times 2 + 2 \times 2 + 12 + 16}} \times 100\% = 46,67\% \\
\Rightarrow \text{ Chất có nồng độ N cao nhất là $(NH_2)_2CO$ }
\end{array}\)
