What is the ruling on someone who eats or drinks while uncertain about the arrival of dawn, then later finds out that dawn had not yet broken?

If a person does this, their fast remains valid, as it is confirmed that they ate during the night. Similarly, if someone eats while uncertain and remains unsure whether they ate before or after dawn, their fast is still valid. This is based on the maxim of Sharia Law, which states: "Certainty is not removed by doubt." Certainty, here, is the presence of night, and the doubt concerns the arrival of dawn. Therefore, one relies on certainty and disregards doubt.

Is an elderly or chronically ill person required to pay additional fidyah if they delay it beyond the first year?

Is Zakah (obligatory charity) due on leased property, and how is it calculated?

Zakah isn`t due on the leased property itself, but on the saved income from that property if it reached Nissab (minimum amount liable for Zakah), and a whole lunar year had lapsed over saving it.

What should someone do if they fasted for 30 days in their country, then traveled to a place where people are still fasting?

If a person completes 30 days of fasting in their country and then travels to another country where people are still fasting, they should continue fasting with them until they observe Eid. Even if they have already completed 30 days, he/she should abstain from eating and drinking and join the people of that country because he/she has now become part of that community.