Which of the following formats could lead to an invalid variable name in SAS?

In SAS, valid variable names must adhere to specific rules. A valid variable name must start with a letter (A-Z or a-z) or an underscore (_), followed by any combination of letters, numbers (0-9), or underscores. The name cannot start with a number, nor can it contain special characters like dollar signs ($) or hyphens (-) except for an underscore.

Given these rules, the option "1st_Name" begins with a numeric character, which makes it invalid as a variable name. Variable names cannot start with numbers, rendering this choice the only one that violates the naming conventions.

The other options adhere to the rules. "Name_1" is a valid variable because it starts with a letter and includes an underscore and a number. "Name$" is also valid in SAS since while it contains the dollar sign, it doesn't violate the initial character rule. "Name-1," despite using a hyphen, is conditional upon SAS interpreting that as a numeric expression unless properly assigned. However, to keep it simple, hyphens might require additional considerations since SAS may interpret them in expressions.

Thus, "1st_Name" is definitively the only option that leads to an invalid variable name in SAS.