a)
$A: C_nH_{2n}O$
$C_nH_{2n}O+H_2\xrightarrow{t^o,Ni}C_nH_{2n+2}O$
0,05 : 0,05 : 0,05 (mol)
$n_{H_2}=\dfrac{1,12}{22,4}=0,05(mol)$
$M_{A}=\dfrac{3,6}{0,5}=72(g/mol)=14n+16$
=> $n=4$
=> $A:C_{4}H_{10}O$
b)
$CH_3-CH_2-CH_2-CHO:\text{butanal}$
$CH_3-CH(CH_3)-CHO:\text{2-metylpropanal}$