Does zakat become obligatory on an amount of 150,0 deposited in the bank as a savings certificate, if the saver has paid off debts close to this amount, and wishes to help his brother with a portion of this amount exceeding 100,0?

The zakat (definition) on savings, which is a quarter of a tenth (2.5%), must be paid once a year has passed over it, regardless of whether it was intended to help a brother or for other purposes. The determining factor is the presence of the amount when a year has passed, making zakat obligatory on it, even if it was prepared to help relatives, for marriage, or for building. As for debt, the preponderant opinion is that it is deducted from the zakatable wealth, unless the payer of zakat has other non-zakatable wealth that is surplus to his needs, in which case it is considered to offset the debt, and he pays zakat on the wealth he possesses.