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.
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.
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 doubting whether one or two prostrations were performed?
Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
If a worshiper is in doubt regarding the number of units (rak'ahs) or prostrations (sajdahs) performed, he must build upon the minimum (i.e., assume the lower number) and perform the prostration of forgetfulness (Sujud al-Sahw) before the Salam at the end of the prayer. This is based on the report from ‘Ata’ ibn Yasar that the Messenger of Allah ﷺ said: 'When anyone of you is in doubt about his Salat (prayer) and does not know how many he has prayed, three or four (Rak'at) he should cast aside his doubt and base his prayer on what he is sure of. Then, he should perform two prostrations before Taslim (salutation). If he has prayed five Rak'at, they will make his Salat (prayer) an even number for him and if he has prayed exactly four, they (i.e. two prostrations) will be humiliation for the devil..' (Narrated by Abu Dawud).
It is stated in Al-Muqaddimah al-Hadramiyyah: 'If one doubts [whether he performed] a bowing (ruku’), a prostration, or a rak'ah, he must perform it and prostrate [for forgetfulness], even if the doubt is removed before the Salam—unless the doubt is removed before he performs what would potentially be an addition. Thus, if he doubts whether he prayed three or four, he is obligated to build upon the minimum.' And Allah the Exalted knows best.