Tax collected at the time of sale - Rs 1,22,500
Tax collected at the time of purchase = Rs 1,00,500
∴ GST payable = Tax collected at the time of sale - Tax collected at the time of purchase
= Rs 1,22,500 - Rs 1,00,500 = Rs 22,000
Thus, the GST payable by Chetana stores is Rs 22,000.