To update the results field from Fail to Pass in a document, which update document syntax is correct?

The correct syntax for updating a specific field in a MongoDB document is to use the $set operator. This operator is designed to update the value of a field in a document to a specified value. In this case, the goal is to change the results field from "Fail" to "Pass".

When using $set, the format requires an object where the key is the field name you want to update and the value is what you want to set it to. So, in the case of updating the result field, {$set: {result: 'Pass'}} effectively conveys that you want to set the result field to the new value of "Pass".

The other options listed are incorrect as they do not represent valid MongoDB update operators. For instance, $change, $update, and $modify are not recognized operators in MongoDB for updating document fields; thus, they would not function as intended in this context. Understanding and correctly applying the $set operator is crucial for effective data manipulation in MongoDB.