$n_C=n_{CO_2}=\dfrac{6,72}{22,4}=0,3(mol)$

$n_N=2n_{N_2}=\dfrac{2.1,12}{22,4}=0,1(mol)$

$n_H=2n_{H_2O}=\dfrac{2.6,3}{18}=0,7(mol)$

$\Rightarrow n_O=\dfrac{8,9-0,3.12-0,1.14-0,7}{16}=0,2(mol)$

$n_C : n_H : n_O: n_N=0,3: 0,7: 0,2: 0,1=3:7:2:1$

$\Rightarrow$ CTĐGN $(C_3H_7O_2N)_n$

$n_A=n_{O_2}=\dfrac{1,6}{32}=0,05(mol)$

$\Rightarrow M_A=\dfrac{4,45}{0,05}=89$

$\Rightarrow n=1$

Vậy CTPT là $C_3H_7O_2N$

$\text{Gọi CTPT (A)} C_xH_yO_zN_t$

$m_C=12n_{CO_2}=12.\dfrac{6,72}{22,4}=3,6g$

$m_H=2n_{H_2O}=2.\dfrac{6,3}{18}=0,7g$

$m_N=28n_{N_2}=28.\dfrac{1,12}{22,4}=1,4g$

$m_O=m_A-m_C-m_H-m_N=3,2g$

$\text{LTL} x:y:z:t = \dfrac{m_C}{12}:\dfrac{m_H}{1}:\dfrac{m_O}{16}:\dfrac{m_N}{14}$

$=0,3:0,7:0,2:0,1=3:7:2:1$

$\text{CTPT (A)} (C_3H_7O_2N)_n$

$\text{Ta có} V_A=V_{O_2}$

$\Rightarrow n_A=n_{O_2}=\dfrac{1,6}{32}=0,05mol$

$\Rightarrow M_A=\dfrac{4,45}{0,05}=89 g/mol$

$\text{Có} (C_3H_7O_2N)_n=89$

$\Rightarrow 89n=89 \Rightarrow n=1$

$\text{Vậy CTPT (A)} C_3H_7O_2N$