Where closing stock is undervalued, the effect is?

When the closing stock is undervalued, it means that the value assigned to the remaining inventory at the end of a financial period is lower than its actual worth. This has an effect on the calculation of the cost of goods sold (COGS), which is the cost of the products that were sold during the period. If the closing stock is undervalued, the COGS will be overstated, which in turn will decrease the gross profit. This is because the cost of goods sold is subtracted from the revenue to calculate the gross profit. If the COGS is higher than it should be, then the gross profit will be lower. An undervalued closing stock doesn't affect the purchases made during the period, as the value of the inventory is determined at the end of the period, after the purchases have already been made. Therefore, the correct answer is "a decrease in gross profit".