Is zakat obligatory upon the owner of a commercial shop whose capital is 40,000 Riyals, and it is his sole source of income from which he spends on his family, and nothing remains after covering basic expenses?

Zakat is obligatory on the value of commercial store goods upon the completion of a full year (hawl) if they reach the minimum threshold (nisab). The goods present in the store are appraised when the hawl is completed. If they reach the nisab, one-quarter of one-tenth (2.5%) of their value is to be given as zakat. If the value is less than the nisab, there is no zakat due on them. The nisab is equivalent to 85 grams of gold or 595 grams of silver.