For those things upon which Zakāt is obligatory, after having paid Zakāt on them, if the [Khums] year passes and they exceed his expenses for the year, its [Khums] must be paid.
Zakāt applies to nine things: 1) wheat 2) barley 3) dates 4) raisins 5) gold 6) silver 7) camels 8) cows, and 9) sheep. If someone owns one of these nine, and certain conditions are met, he/she must give the allocated amount to be disposed for the purposes specified.
Therefore, if a person is in possession of the abovementioned items, wherever the conditions are met, they must pay Zakāt on them. However, if someone owns assets or property other than those mentioned, then through other conditions, Khums would be due [on that property].
Another difference between Khums and Zakāt is that the latter is not payable to the poor amongst the Hashemite Sādāt (decedents of bani Hashim), on the contrary; half of Khums is allocated for poor Hashemite Sādāt.
For those whom Zakāt is obligatory, they can pay their dues to close-ones who fall under the category of being poor, however it is not permissible to use the Zakāt to pay the expenditures of those whom they are responsible for [through obligation], such as one’s children. In addition, an alternative use for the Zakāt is to pay it to the representative of the Imām, or someone who has been given the responsibility by the Imām to collect and preserve the Zakāt, also to keep an account of it and [eventually] to deliver it to the Imām, his representative, or the poor.
Essentially, paying the Zakāt has no relation to paying taxes (the two are not connected); taxes are something collected by all governments to fulfill their expenditures.
 Tawdih al-Masa’il (annotated by Imam Khomeini), vol. 2, pg. 10; also, see: Sirat al-Najat (of Ayatullah Khu’i with Ayatullah Tabrizi’s annotations), vol. 3, pg. 119, question 360, Muntakhab Press, Qum, 1416 AH: “إذا تملّک الغلات بالزراعة أو باستثمار الأشجار، فتتعلّق الزکاة بها قبل تعلّق الخمس، فیزکّی أولا ثم ان بقی المزکّى الى آخر السنة زائدا عن مئونته، و زائدا على المال الذی صرفه فی تحصیله فیجب فیه الخمس”.
 The Zakāt of gold and silver is obligatory if they are stamped and are commonly used for in transactions. See: Tawdih al-Masa’il (annotated by Imam Khomeini), vol. 2, pg. 130.
 Tawdih al-Masa’il (annotated by Imam Khomeini), vol. 2, pg. 107.
 Nonetheless, the seyed/sādāt can receive Zakāt from another seyed/sādāt under certain circumstances; the grand maraji’ state: “The seyed/sādāt cannot receive Zakāt from non-seyeds/sādāt, but if receiving khums and other monetary alms don’t suffice him in his expenses and he has no choice but to rely on Zakāt as well, he can take it from a non-seyed/sādāt.” See: Tawdih al-Masa’il (annotated by Imam Khomeini), vol. 2, pg. 155.
 Tawdih al-Masa’il (annotated by Imam Khomeini), vol. 2, pg. 155.
 Tawdih al-Masa’il (annotated by Imam Khomeini), vol. 2, pg. 152.