Under absorption of overhead expenses in cost accounting results in _________.

Under absorption of overhead expenses in cost accounting refers to the allocation of overhead costs to the cost of production. When overhead expenses are absorbed into the cost of production, it results in a higher portion of overhead being included in the cost of goods sold.

This leads to a higher total cost of production, which in turn decreases the per unit cost of production. When the cost of production decreases, the profit margin per unit increases, resulting in an increase in costing profit.

Therefore, the correct option is increase in costing profit.