Q 1: What is the ruling on
depositing money in banks for a fixed profit?
Depositing money in banks in return for a fixed interest is not permissible because this is a Riba (usury/interest) - based contract. Allah (Exalted be He) says,
...whereas Allâh has permitted trading and forbidden Ribâ (usury).
O you who believe! Be afraid of Allâh and give up what remains (due to you) from Ribâ (usury) (from now onward), if you are (really) believers.
And if you do not do it, then take a notice of war from Allâh and His Messenger but if you repent, you shall have your capital sums. Deal not unjustly (by asking more than your capital sums), and you shall not be dealt with unjustly (by receiving less than your capital sums).
This amount of money that the depositor receives is not lawful and contains no blessing. Allah (Exalted be He) says,
Allâh will destroy Ribâ (usury) and will give increase for Sadaqât (deeds of charity, alms, etc.)
This kind of Riba contains Riba Al-Nasi'ah (usury of delay, conditional excess for delay of payment) and Riba Al-Fadl (usury of excess, selling an item for another of the same type, on the spot, but in excess) because the depositor pays a sum of money to the bank in order for it to stay there for a defined period of time in return for a defined profit.