Final answer:
The key budgeting element on which the entire operating budget is based is the revenue or income that the government expects to receive in taxes and other sources, and the expenditures or spending that the government plans to make.
Step-by-step explanation:
The key budgeting element on which the entire operating budget is based is the revenue or income that the government expects to receive in taxes and other sources. This includes the amount of money the government anticipates collecting from individuals, businesses, and other entities. Additionally, the operating budget also considers the expenditures or spending that the government plans to make, which includes investments in infrastructure, social programs, defense, and various other areas.