Em tham khảo nha :

\(\begin{array}{l}
1)\\
CTHH\,A:{C_x}{H_y}\\
{n_A} = \dfrac{V}{{22,4}} = \frac{1}{{22,4}} = 0,0446mol\\
{M_A} = \dfrac{m}{n} = \frac{{1,25}}{{0,446}} = 28dvC\\
\% C = \dfrac{{x{M_C}}}{{{M_A}}} \times 100\%  = 85,71\% \\
 \Rightarrow x = \dfrac{{0,8571 \times 28}}{{12}} = 2\\
\% H = \dfrac{{y{M_H}}}{{{M_A}}} \times 100\%  = 14,29\% \\
 \Rightarrow y = \dfrac{{0,1429 \times 28}}{1} = 4\\
CTHH\,A:{C_2}{H_4}\\
2)\\
CTHH\,B:{C_x}{H_y}\\
\dfrac{{x{M_C}}}{{y{M_H}}} = \frac{{80\% }}{{20\% }} \Rightarrow \dfrac{x}{y} = \dfrac{{80}}{{20 \times 12}} = \dfrac{1}{3}\\
 \Rightarrow x = 2;y = 6\\
CTHH:{C_2}{H_6}\\
3)\\
CTHH\,C:{C_x}{H_y}{O_2}\\
\dfrac{{x{M_C}}}{{y{M_H}}} = \dfrac{{40\% }}{{6,67\% }} \Rightarrow \dfrac{x}{y} = \dfrac{{40}}{{6,67 \times 12}} = \dfrac{1}{2}\\
 \Rightarrow x = 1;y = 2\\
CTHH:C{H_2}{O_2}\,hay\,HCOOH
\end{array}\)

Đáp án:

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