Is zakat obligatory on money that has reached the nisab and a full year has passed, even if its value has decreased from its initial amount, provided it still remains within the limits of the nisab, and the condition of growth has not been met in it?

It is not a condition for Zakat that wealth genuinely increases. Rather, scholars have sought wisdom in allocating Zakat to specific types of wealth that are expected to grow and bear fruit, namely: gold and silver (and banknotes), produce from the earth, livestock, and trade goods. Scholars have unanimously agreed on the obligation of Zakat on these types of wealth. They either achieve actual growth or are capable of growth. Zakat was legislated for growing wealth to make its payment easier. Therefore, if a Muslim possesses the nisab and a year has passed, Zakat becomes obligatory, even if the wealth decreased from the previous year or the trade was unprofitable, as long as it has not fallen below the nisab.