Final answer:
In a parliamentary government, the chief executive is chosen by the legislature. In a presidential government, the chief executive is directly elected by the citizens.
Step-by-step explanation:
In a parliamentary government, the chief executive, usually called the prime minister, is selected by the legislative branch (parliament) after citizens elect the members of the legislature.
On the other hand, in a presidential government, citizen voters directly choose the chief executive, usually called the president.
So, in summary, the basic difference between a parliamentary and presidential government, in regards to the selection of the chief executive, is that in a parliamentary government, the chief executive is chosen by the legislature, while in a presidential government, the chief executive is directly elected by the citizens.