Are minors(persons under the age of puberty) obliged to fast?

A male under the age of puberty isn`t required to fast, but his guardian should order him to fast if he was able to endure the hardship until he gets used to it.

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

Zakah isn`t due on the rented 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 is the ruling on using bank cards such as Visa and MasterCard?

All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upo all of his family and comapnions.

It is permissible to use such cards in accordance with the following conditions : 1- The issuing body does not stipulate collecting interest upon late payments. 2- The merchant does not increase the price of the goods due to an increase in the commission collected from him by the card issuer.3- The purchased item(s) should not be gold , silver or currency in case the card is not covered. And Allah Knows Best.

How to pay Zakah(obligatory charity) on articles of merchandise?

Articles of merchandise are estimated by their whole sale market price at the end of each lunar year, and (2.5%) of their value is paid as Zakah whether it(value) went up, or down compared to actual purchasing price, and whether the increase(profit) was in the article itself such as an increase in the animal`s weight, or in the prices themselves.