CH3CH3: this is a formula for ethane where all protons are
equivalent with respect to each other so we will get one signal
corresponding to all six protons.
CH3COCH3: In this chemical formula of Acetone both methyl
protons are equivalent with respect to carbonyl group in the
middle. Hence this compound will also give one signal for all 6
protons.
CH3CH2CH2COH: This is a formula for butyl aldehyde. This
compound contains 4 different types of proton.
Aldehyde proton from COH group
One doublet signal for CH2 protons attached to Carbonyl
carbon
Second Doublet for CH2 attached to CH2 group
Triplet signal for 3 protons from last methyl group in butyl
aldehyde formula.