`a)`

`n_{CO_2}=x(mol);n_{H_2O}=y(mol)`

`->44x+18y=16,4(1)`

BTNT O: `n_{O_2}=x+0,5y(mol)`

BTKL: `3,6+32(x+0,5y)=16,4(2)`

`(1)(2)->x=0,25;y=0,3`

`n_{CO_2}<n_{H_2O}->A:C_nH_{2n+2}`

`n_A=n_{H_2O}-n_{CO_2}=0,05(mol)`

`->M_A=14n+2={3,6}/{0,05}=72`

`->n=5`

`->A:C_5H_{12}`

`CH_3-CH_2-CH_2-CH_2-CH_3:` pentane

`CH_3-CH(CH_3)-CH_2-CH_3:` 2-methylbutane

`C(CH_3)_4:` 2,2-dimethylpropane

`b)`

`A` là 2-methylbutane `CH_3CH(CH_3)CH_2CH_3`