Is zakat obligatory on the money a student possesses from his allowance given by his father, which fluctuates during the year? If so, how is zakat calculated for this money? What is the nisab at which zakat becomes obligatory? And can zakat be given to Zakat House?

Zakat is obligatory on banknotes if a person fully owns them and a complete year has passed since their acquisition. The money a father gives his son becomes the son's property, and Zakat is obligatory on it. Banknotes are analogous to gold and silver regarding the obligation of Zakat, and their nisab (minimum taxable amount) is estimated at the value of 595 grams of silver, which is equivalent to approximately 1093 Saudi Riyals (according to 2007 prices). If the wealth reaches this nisab and a year passes without it decreasing below it, Zakat becomes obligatory at a rate of 2.5 percent. If the wealth falls below the nisab during the year, Zakat is not obligatory unless it reaches the nisab again, and a new year's calculation begins. It is preferable to pay Zakat if the decrease is minor. Allah Almighty says: (And those who hoard gold and silver and spend it not in the way of Allah – give them tidings of a painful punishment. The Day it will be heated in the Fire of Hell, and therewith will be branded their foreheads, their flanks, and their backs, [it will be said], "This is what you hoarded for yourselves, so taste what you used to hoard.") [At-Tawbah/34-35].