The question is about designing a process model to store the result of an expression rule for every item in a list with the lowest memory footprint. The best design for this purpose is to configure a script task to use a!foreach to iterate over each item in the list, as it allows you to execute an expression rule for each element of an array without creating multiple nodes or subprocesses in the process model. A script task is a node that executes an expression without user interaction, and a!foreach is a function that applies an expression to each element of an array and returns an array of results. The other options are not optimal for this purpose, as they either create more nodes or subprocesses in the process model, which consume more memory and resources. References:

Script Task

a!foreach()