What type of illness that permits breaking the fast in Ramadan?
It is an illness that, if one fasts, there is a fear it may lead to their death or cause unbearable hardship.
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]
What is the ruling on using eye drops while fasting?
Eye drops do not break the fast, even if the taste reaches the throat, because the eye is not an open passage to the body cavity.
What is the ruling on taking a medication tablet sublingually during the daytime in Ramadan?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Taking a medication tablet sublingually (under the tongue) during the daytime in Ramadan does not invalidate the fast, since it does not reach the internal cavity (al-jawf) through an open passage.
However, if the tablet dissolves and any part of it is swallowed, then the fast is broken.
And Allah, the Exalted, knows best.