Em tham khảo nha :

\(\begin{array}{l}
85)\\
CTHH:C{u_x}O\\
\text{Trong hợp chất , Cu chiếm 80% về khối lượng}\\
x{M_{Cu}} = 80\%  \times {M_{C{u_x}O}}\\
 \Rightarrow 64x = 0,8 \times 80\\
 \Rightarrow x = \dfrac{{64}}{{64}} = 1\\
 \Rightarrow CTHH:CuO\\
88)\\
CTHH:{C_x}{H_y}\\
{M_{{C_x}{H_y}}} = 8 \times {M_{{H_2}}} = 16dvC\\
\text{Trong hợp chất , C chiếm 75% về khối lượng}\\
x{M_C} = 75\%  \times {M_{{C_x}{H_y}}}\\
 \Rightarrow x = \dfrac{{0,75 \times 16}}{{12}} = 1\\
 \Rightarrow {M_C} + y{M_H} = 16\\
 \Rightarrow y = 16 - 12 = 4\\
 \Rightarrow CTHH:C{H_4}\\
89)\\
a)\\
CTHH\,A:N{a_x}C{l_y}\\
y{M_{Cl}} = 60,68\%  \times {M_A}\\
 \Rightarrow y = \dfrac{{0,6068 \times 58,5}}{{35,5}} = 1\\
 \Rightarrow x{M_{Na}} + {M_{Cl}} = 58,5\\
 \Rightarrow x = \dfrac{{58,5 - 35,5}}{{23}} = 1\\
 \Rightarrow CTHH:NaCl\\
b)\\
CTHH\,B:N{a_x}{C_y}{O_z}\\
x{M_{Na}} = 43,4\%  \times {M_B}\\
 \Rightarrow x = \dfrac{{0,434 \times 106}}{{23}} = 2\\
y{M_C} = 11,3\%  \times {M_B}\\
 \Rightarrow y = \dfrac{{0,113 \times 106}}{{12}} = 1\\
z{M_O} = 45,3\%  \times {M_B}\\
 \Rightarrow z = \dfrac{{45,3 \times 106}}{{16}} = 3\\
 \Rightarrow CTHH:N{a_2}C{O_3}\\
c)\\
CTHH\,C:{K_x}{N_y}{O_z}\\
x{M_K} = 38,61\%  \times {M_C}\\
 \Rightarrow x = \dfrac{{0,3861 \times 101}}{{39}} = 1\\
y{M_N} = 13,86\%  \times {M_C}\\
 \Rightarrow y = \dfrac{{0,1386 \times 101}}{{14}} = 1\\
z{M_O} = 47,53\%  \times {M_C}\\
 \Rightarrow z = \dfrac{{0,4753 \times 101}}{{16}} = 3\\
 \Rightarrow CTHH:KN{O_3}\\
d)\\
CTHH:N{a_x}{S_y}{O_z}\\
x{M_{Na}} = 36,508\%  \times {M_D}\\
 \Rightarrow x = \dfrac{{0,36508 \times 126}}{{23}} = 2\\
y{M_S} = 25,4\%  \times {M_D}\\
 \Rightarrow y = \dfrac{{0,254 \times 126}}{{32}} = 1\\
z{M_O} = 38,092\%  \times {M_D}\\
 \Rightarrow z = \dfrac{{0,38092 \times 126}}{{16}} = 3\\
 \Rightarrow CTHH:N{a_2}S{O_3}
\end{array}\)