Is Zakat obligatory on an unstable daily wage, and is it permissible to give it to one's parents?

Zakat is obligatory on a salary if it reaches the nisab either by itself or by combining it with other money or trade goods, and a full year has passed over it. It is not permissible to give zakat to one's parents because their maintenance is obligatory. Rather, it should be given to those whose maintenance is not obligatory, such as the poor, the needy, and others from the eight categories mentioned in the Quran.