Is the niṣāb calculated based on the price of 21-karat gold, or 24-karat gold?
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.
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.
The one paying zakāh may assess/calculate the niṣāb using any of the aforementioned gold karats [i.e., he may choose whichever karat standard he wishes for the purpose of the calculation]. And Allah, the Exalted, knows best.
My husband discloses all our marital disputes to his family. What is the ruling of Islamic Law on this?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is impermissible to divulge spousal secrets or expose one another's faults, whether during the subsistence of the marriage or after its dissolution. The foundational principle governing marital relations is that it is built upon confidentiality and mutual affection. Divulging marital secrets constitutes a breach of trust and a grave sin.
A husband ought not to resort to his family to complain about his wife over every dispute, nor is the reverse permissible for the wife, especially when such actions lead to stirring up malice and animosity between the spouses or between their respective families.
Islam has enjoined the preservation of secrets in general and commanded against revealing them; safeguarding the privacy of the home holds an even greater priority. And Allah Almighty knows best.
Can I start fasting based on the moon sighting of another country?
You must follow the moon sighting of the country you are in.
What is the ruling if a postpartum woman becomes pure before forty days; are acts of worship obligatory upon her, and is she permissible for her husband?
If the postpartum woman becomes definitely pure before forty days, she must perform the ritual bath and perform acts of worship as a pure woman does. What was prohibited for her also becomes permissible, so she becomes permissible for her husband after her bath. The minimum duration for postpartum bleeding is a moment (an instant), and its usual maximum is forty days. Reaching forty days is not a condition; rather, it is sufficient for the blood to stop or to see the white discharge (qassa bayda'). And Allah the Almighty knows best.