Answer
a/ alkane
b/alkene
c/ alkyne and aromatic
Work Step by Step
Focus on the region of
1/ saturated C-H for alkane around 3000 - strong signals
2/ see if there is any C=C (above 3000) or =C-H for alkene (around 1640)
3/ terminal alkyne usually at around 3300 strong signal and small signal at 2100 only if there is dipole moment at C-C triple bond
4/Aromatic will be small broad signal around 3050
