How is the niṣāb (minimum threshold) of gold calculated when one owns gold of multiple different karats?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Zakāh is obligatory on cash and on gold designated for saving or for trade, provided the total reaches the niṣāb (minimum threshold liable for Zakah), and a full ḥawl (lunar year) has elapsed over it. The niṣāb is (85) grams of 24-karat gold; for 21-karat gold, the niṣāb equals (97) grams; and for 18-karat gold, it equals (113) grams.
If one owns gold of multiple different karats, the person paying zakāh should calculate the monetary value of all the gold he owns, combining these values together to determine whether the total reaches the niṣāb. He then pays zakāh on this combined monetary value, once the total reaches the niṣāb. The relied-upon position is to calculate the zakāh based on the buying price [i.e., the price the gold merchant would pay the owner to purchase the gold from him] on the day the zakāh obligation is due. And Allah, the Exalted, knows best.
What is the ruling on the use of an inhaler by a *muḥrim* (a person in the state of *iḥrām*)? [An inhaler is a medicinal device used for inhalation, containing various herbal ingredients.]؟
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is permissible for the muḥrim (a person in the state of iḥrām) to use incense (bakhūr), sprays, and inhalers that contain aromatic substances for the purpose of treatment, because the intention is medical treatment, not the use of perfume (taṭayyub). No expiation (fidyah) is required of him for doing so.
It is stated in Ḥāshiyat al-Bujayrimī ʿalā al-Khaṭīb (Vol.2/p.455): “That which is intended for eating or for medical treatment, even if it has a pleasant scent, such as apples, spikenard (sunbul), and the various fragrant spices such as mastic (muṣṭakā), is not forbidden, and no fidyah is due for it, because what is intended for eating or treatment carries no fidyah.”. And Allah Almighty knows best.
Can someone who begins a voluntary fast break it?
It is preferable for someone who begins an act of worship not to break it.
Allah the Exalted has said {what means}: "and let not your [good] deeds come to nought!" [Muhammad/33].
However, if a person starts a voluntary fast (nafl) and needs to break it, they are going against what is preferable, but there is no sin upon them.
Are school exams a valid excuse for breaking the fast in Ramadan?
School and university exams are not considered a valid excuse for breaking the fast, as most students take their exams while fasting without experiencing extreme hardship. Fasting does not conflict with exam preparation, and a Muslim seeks strength in obedience to Allah for both worldly and spiritual matters.