Does using a respiratory device (oxygen) affect the validity of fasting?
Using an oxygen device does not affect the validity of fasting because oxygen is a gas with no physical substance.
However, if medicinal substances with physical particles are added to the oxygen, its use would break the fast, as it enters the body cavity through a natural passage.
Is it permissible to offer an Udhiyah on behalf of another without their permission?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is not permissible for a person to offer a sacrifice (Udhiyah) on behalf of someone else without their permission, except in the following cases: if he sacrifices on behalf of the members of his household, if a guardian sacrifices from his own wealth on behalf of his ward, or if the Imam (ruler) sacrifices from the public treasury (Bayt al-Mal) on behalf of the Muslims. And Allah the Almighty knows best.
Is it permissible to offer mandatory prayer while sitting?
All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions. Standing up is a pillar in the mandatory prayer and the prayer is not valid without it unless one cannot do it. As for Nafila (supererogatory prayer), one can perform it in the state of sitting even if he/she can stand, but his/her reward is half the reward of the person who prays while standing if he/sh has no legal excuse for such an act. And Allah Knows Best.
What is the meaning of the Udhiyah?
Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
The Udhiyah (Sacrificial Offering) refers to the livestock (An'am) that is slaughtered as an act of drawing closer to Allah the Almighty. This takes place on the day of Eid al-Adha (the 10th of Dhu al-Hijjah) and during the three days of Tashreeq that follow the day of Eid. And Allah the Exalted knows best.