Which of the following is a valid variable name in Python?

Out of the given options, my_variable is the only valid variable name in Python.
A variable is a name assigned to a value or data in programming. In Python, we have certain rules for naming variables.
Rule 1: Variable names must start with a letter (a-z, A-Z) or an underscore (_).
Rule 2: After the first character, variable names can consist of letters, numbers (0-9), or underscores (_). Symbols, such as $ or -, are not allowed in variable names.
Rule 3: Variable names are case-sensitive, so "my_variable" and "My_variable" would be considered as different variables.
Following these rules, we find that the valid variable name is my_variable. It starts with a letter, followed by letters and underscores.
The other options, my_variable$, my-variable, and 1my_variable, do not follow the rules mentioned above. They either include symbols ($) or hyphens (-) in the name, or start with a number (1), which is not allowed. Therefore, they are not valid variable names in Python.