The Hachamim instituted a Gezerah not to shake the Lulav and Etrog on Shabbat of Succot. Therefore, the Lulav and Aravot, which have no permissible use, retain a status of Mukse and may not be handled. However, Hacham Ovadia rules that the Hadasim and Etrog are not Mukse, if one intended to use them for their smell before Shabbat. Since there is no Misva to shake them on Shabbat, they are not designated exclusively for the Misva and may be used for smelling. Regarding the Etrog, there is a question as to which Beracha is made for its fragrance, and that is why it is not used for its fragrance during the year. Nevertheless it is not Mukse, since one can make a Beracha on a different fruit, having in mind to exempt the Etrog.
The Lulav and Aravot are Mukse on the Shabbat of Succot, whereas the Etrog and Hadasim are not, since they may be used for their smell.