What is the semi-circular structure attached to the Holy Kabah?
The semi-circular structure attached to the Holy Kabah is Hijr Al-Kabah (is a low wall originally part of the Kabah) and passing behind it is an obligation while making Tawaf because it is a part of the Holy Kabah. And Allah Knows Best.
What are the conditions that must be met for the 'aqīqah to be valid?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
The 'aqīqah is like the recommended uḍḥiyyah in terms of the type of animal, its age, and its required characteristics — since it is a recommended slaughter and therefore resembles the uḍḥiyyah in its rulings.
It is agreed upon without any difference of opinion that the 'aqīqah is not valid with any animal other than livestock (al-na'am — camels, cattle, and sheep). Likewise, an animal with a disqualifying defect — such as obvious illness, lameness, or blindness in one eye — does not suffice, as has previously been explained in the rulings of the uḍḥiyyah. And Allah Almighty knows best.
Is it a condition that a woman should untie her locks while making Ghusl (ritual bath)?
Ghusl from Janabah (ritual impurity), or menstruation obligates that water reaches the roots of the hair in order for the Ghusl to be valid, but if it doesn`t, then hair locks must be untied for water to reach them, and for Ghusl to become valid.
What is the ruling on the white discharge (*Al-Qassat al-Bayda'*) if it is in a very small amount—is it considered a sign of purity?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
Among the signs of purity (Tahr) for a woman is the white discharge (Al-Qassat al-Bayda'), which is a clear, pure white fluid, regardless of whether it is minimal in quantity, or complete dryness (Jafaf), wherein secretions cease entirely such that if a white cotton cloth is inserted, it comes out completely clean. Once a woman observes either of these two signs, she has attained ritual purity.
Furthermore, another sign of purity is when the duration of the menstrual period exceeds the maximum limit of menstruation, which is fifteen days. If it exceeds this period, it becomes evident that she is experiencing non-menstrual bleeding (Istihadah).