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.
Which is better during the day in Ramadan: reciting the Quran or performing voluntary prayers?
A Muslim should establish a daily schedule for reciting the Quran in Ramadan.
Once they have completed their daily portion (known as a wird or hizb), they can engage in other acts of worship, including voluntary prayers (nawafil). Prayer itself is called "Quran", because a significant part of it involves reciting the Quran.
Allah says: "BE CONSTANT in [thy] prayer from the time when the sun has passed its zenith till the darkness of night, and [be ever mindful of its] recitation at dawn: for, behold, the recitation [of prayer] at dawn is indeed witnessed [by all that is holy]." [Al-Isra`/78]
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.
Is it valid to have Suhoor before sleeping, even if it is before midnight?
Suhoor refers to the pre-dawn meal eaten after midnight to help a Muslim endure fasting. The closer it is to Fajr, the better.
The Prophet ﷺ said: "My Ummah will remain upon goodness as long as they hasten to break the fast and delay Suhoor." [Narrated by Ahmad]
This is because delaying Suhoor makes it more effective in providing strength for worship. However, if there is a risk of Fajr entering while eating, one should refrain from Suhoor out of caution.
The Prophet ﷺ said: "Leave what makes you doubt for what does not make you doubt." [Narrated by Al-Tirmidhi]