Qualitative observations provide us with the qualitative details about an object. Such details can not be expressed in numbers or as measurements. Apple is fresh, cut is deep are an examples of some of the qualitative details.
Quantitative observations provide us numerical details about an object under study. Weight, length, volume are some of the qualitative observations. Inference is used to give details about logical interpretation based on previous knowledge and experiences. Hypothesis consists of observations with a scientific explanation.
Hence, the correct option is (a) quantitative observation.