Which scenario would allow e-filing if one spouse lacks an SSN or ITIN?

The scenario where one spouse has an SSN while the other does not allows for e-filing under certain conditions. Specifically, if one spouse possesses a valid Social Security Number and the other spouse does not have either an SSN or an ITIN, they may still file electronically. The IRS allows this because the presence of a valid taxpayer identification number (the SSN in this case) from one spouse enables the electronic processing of the return, even if the other spouse's information is not complete.

Filing with a dependent child who has an ITIN (the second choice) does not meet the criteria since the e-filing requirement is focused on the marital filing status and the identification of the spouses themselves, not dependents. The third choice, where a couple is filing separately, generally requires both spouses to provide identifying numbers; thus, it also does not allow e-filing if one lacks the necessary identification. Lastly, "None of the above" cannot be the correct answer as the first scenario does indeed support e-filing based on the provisions allowed by tax regulations.