This is because First Name is a variable name format that would be problematic if used in most of the data software programs, such as Excel, SQL, or Python. This is because First Name contains a space between two words, which could cause confusion or errors in the data software programs, as they might interpret the space as a separator or a delimiter between two different variables or values, rather than as part of a single variable name. For example, in SQL, a space is used to separate keywords, clauses, or expressions in a statement, such as SELECT, FROM, WHERE, etc. Therefore, using First Name as a variable name in SQL could result in a syntax error or an unexpected result. The other variable name formats would not be problematic if used in most of the data software programs. Here is why:

First_Name_ is a variable name format that uses an underscore (_) to separate two words, which is a common and acceptable practice in most of the data software programs, as it helps to improve the readability and clarity of the variable name. For example, in Python, an underscore is used to follow the PEP 8 style guide for naming variables, which recommends using lowercase letters and underscores for multi-word variable names.

FirstName is a variable name format that uses camel case to separate two words, which is another common and acceptable practice in most of the data software programs, as it helps to reduce the length and complexity of the variable name. For example, in Excel, camel case is used to follow the VBA naming conventions for naming variables, which recommends using mixed case letters for multi-word variable names.

First_Name is a variable name format that also uses an underscore (_) to separate two words, which is also a common and acceptable practice in most of the data software programs, as it helps to improve the readability and clarity of the variable name. For example, in SQL, an underscore is used to follow the ANSI SQL naming standards for naming variables, which recommends using lowercase letters and underscores for multi-word variable names.