Primary alcohol is the only alcohol which can fully oxidise as it first oxidises to an aldehyde and this can be further oxidised to a carboxylic acid. This is not possible with 20 alcohols as they oxidise to ketones which cannot be further oxidised due to the lack of a place for the oxygen to bond. 30 cannot oxidise whatsoever.To obtain a carboxylic acid from a primary alcohol you must add oxidising agent for example potassium dichromate (K2Cr2O7/H+ ). Then place this solution under reflux and the resulting product will be a carboxylic acid.