(a) postman works in an organized sector because he is working in a government organization.
(b) If the textile industry is owned by a private individual or firm, then it can be categorized under the unorganized sector. But, if the textile industry is owned or controlled by the government, then it can be categorized under the organized sector.
(c) a plumber is employed on his/her own. So, a plumber works in an unorganized sector.