What is the ruling on not fulfilling a vow?
A vow is a commitment towards Allah, The Almighty, and so, it should be observed as much as possible, and it is impermissible to take it lightly. Allah, The Exalted, Says –in commending the believers (What means): "(Because) they perform the vow and fear a day whereof the evil is wide-spreading." [Al-Insan/7].
What is the ruling on the unification of Adhan?
All perfect praise be to AllahThe Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions. The unified Adhan is an act of Sunnah performed on behalf of a city's population. In addition, any Masjid that doesn’t have a Mua'than (The person who calls for prayers) and doesn`t raise the Adhan misses the reward of this great act. This is because Adhan should be raised for every group of people. However, the unified Adhan should be called in one Masjid and heard through all other Masjids. And Allah Knows Best.
Is it permissible for a sick person to pray while sitting on a chair?
All perfect praise be to Allah, The Lord of the Worlds It is permissible for a sick person, who is unable to stand up, to offer prayer while sitting on a chair. If he/she was unable to prostrate while on the chair, the he/she should pray while sitting on the ground, but if he/she was neither able to bow (Roku),nor to prostrate, then he can do them while sitting on the chair. And Allah Knows Best.
Is it permissible for someone who has forgotten to mention the supplication pertaining to answering the call of nature to say it while in the toilet?
It is disliked for a Muslim to mention Allah while in the toilet, but he/she may recall the supplication in his/her head without uttering it; that is in case he/she had forgotten mentioning it before entering the toilet.