Which account posting rule that impacts financials will be set up during a payroll first deployment?

The correct choice is Retained Earnings because, during a payroll first deployment, financials need to account for the net effect of payroll transactions on the income statement and balance sheet. Retained Earnings accounts are crucial as they reflect the accumulated net income of the business, which is impacted by payroll expenses. Payroll affects profitability, and thus any expenses incurred through payroll need to be recorded properly to reflect their impact on the organization's financial health.

When payroll transactions occur, the expenses recorded will eventually flow into the net income calculation, subsequently affecting retained earnings. This ensures that the organization's financial statements accurately depict its performance over time. In contrast, while other accounts such as payables, undeposited payments, and accrued expenses are relevant to payroll processing, they do not directly impact the net income on the income statement in the same way that retained earnings do during the initial payroll setup.