\(\dfrac{M_A}{M_{H_2}}=31\) \(\Rightarrow M_{H_2}=31.2=62\) \((g/mol)\)

Đốt cháy A tạo ra CO₂ và H₂O

`=>` Trong A có C,H và có thể có O

\(m_{O_2}=\left(\dfrac{2,8}{22,4}\right).32=4\left(g\right)\)

\(m_{CO_2}=\left(\dfrac{2,24}{22,4}\right).44=4,4\left(g\right)\)

BTKL: \(m_A=m_{CO_2}+m_{H_2O}-m_{O_2}=4,4+2,7-4=3,1\left(g\right)\)

Bảo toàn C: \(n_C=n_{CO_2}=\dfrac{2,24}{22,4}=0,1\left(mol\right)\)

Bảo toàn H: \(n_H=2.n_{H_2O}=2.\dfrac{2,7}{18}=0,3\left(mol\right)\)

\(n_O=\dfrac{3,1-\left(0,1.12+0,3.1\right)}{16}=0,1\left(mol\right)\)

Đặt CTTQ A: \(C_xH_yO_z\)

\(x:y:z=0,1:0,3:0,1=1:3:1\)

\(CTĐG:\left(CH_3O\right)n=62\)

              \(\Rightarrow n=2\)

`=>` CTPT A: \(C_2H_6O_2\)

ths nhường đó:33

Chọn D

hahaa

\(M_A=180\) \((g/mol)\)

Gọi CTTQ A: \(C_xH_yO_z\)

\(\Rightarrow x:y:z=\dfrac{40}{12}:\dfrac{6,67}{1}:\dfrac{53,33}{16}\)

                  \(=3,33:6,67:3,33\)

                  \(=1:2:1\)

CTĐG A: \(\left(CH_2O\right)n=180\)

               \(\Rightarrow n=6\)

`=>` CTPT A: \(C_6H_{12}O_6\)

nma hàng cuối \(\sqrt{2}\) xuu nhaa:"))

Đặt \(P=\dfrac{1}{1\times3}+\dfrac{1}{3\times5}+\dfrac{1}{5\times7}+\dfrac{1}{7\times9}+\dfrac{1}{9\times11}\)

\(\Rightarrow2P=\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+\dfrac{2}{9\times11}\)

\(\Rightarrow2P=\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\)

\(\Rightarrow2P=\dfrac{1}{1}-\dfrac{1}{11}\)

\(\Rightarrow2P=\dfrac{10}{11}\)

\(\Rightarrow P=\dfrac{5}{11}\)

\(n_{H_2O}=\dfrac{3,6}{18}=0,2\left(mol\right)\)

\(SO_3+H_2O\rightarrow H_2SO_4\)

0,2         0,2          0,2      ( mol )

\(V_{SO_3}=0,2.22,4=4,48\left(l\right)\)

\(m_{H_2SO_4}=0,2.98=19,6\left(g\right)\)

\(\dfrac{2}{\sqrt{3}}+\dfrac{\sqrt{2}}{3}+\dfrac{2}{\sqrt{3}}.\sqrt{\dfrac{5}{12}-\dfrac{1}{6}}\)

\(=\)\(\dfrac{2}{\sqrt{3}}+\dfrac{\sqrt{2}}{3}+\dfrac{2}{\sqrt{3}}.\sqrt{\dfrac{1}{4}}\)

`=`\(\dfrac{2}{\sqrt{3}}+\dfrac{\sqrt{2}}{3}+\dfrac{2}{\sqrt{3}}.\dfrac{1}{2}\)

\(=\dfrac{2}{\sqrt{3}}\left(1+\dfrac{1}{2}\right)+\dfrac{\sqrt{2}}{3}\)

\(=\dfrac{2}{\sqrt{3}}.\dfrac{3}{2}+\dfrac{\sqrt{2}}{3}\)

\(=\dfrac{3}{\sqrt{3}}+\dfrac{\sqrt{2}}{3}\)

\(=\dfrac{3\sqrt{3}+\sqrt{2}}{3}\)