Final answer:
The question does not provide enough context about the PLC program to accurately determine the state of the timer and counter after 'T4:2.ACC=20' is reached. An understanding of the specific program logic is needed to make this prediction.
Step-by-step explanation:
The question asks what happens on the next scan after 'T4:2.ACC=20', assuming that by 'T4:2' we refer to a timer in a programmable logic controller (PLC), 'ACC' is the accumulated value, and 'PB' is a push button input. If 'T4:2.ACC=20' has been reached, this means the timer has accumulated to its preset value.
In general, once a timer has reached its preset value, it would typically set its done bit ('DN') to true, and if the timer is enabled ('EN') it remains true until reset. The counter value ('C5:1/CU') would depend on separate logic conditions in the program. It's important to be familiar with the logic in the PLC program to accurately predict the next state of these elements.