`a)`

BTNT C: `n_C=n_{CO_2}={6,72}/{22,4}=0,3(mol)`

BTNT H: `n_H=2n_{H_2O}=2.{5,4}/{18}=0,6(mol)`

`->n_C:n_H=0,3:0,6=1:2`

`->` CTN: `(CH_2)_n`

`M_X=14n=1,5.28=42`

`->n=3`

`->X:C_3H_6`

`b)`

`CH_2=CH-CH_3`

`\color{gold}{#aether}`

`a)`

Bảo toàn `C:n_C=n_{CO_2}=(6,72)/(22,4)=0,3` `mol`

Bảo toàn `H:n_H=2n_{H_2O}=2.(5,4)/(18)=0,6` `mol`

`n_C:n_H=0,3:0,6=1:2`

`=>` CTĐGN của `A:(CH_2)_n`

$d_{X/N_2}$`=1,5`

`=>M_X=1,5.28=42``(g``/``mol)`

`=>(12+1.2).n=14n=42`

`=>n=3`

`=>X:C_3H_6`

`b)`

CTCT `X:CH_2=CH-CH_3`