In which mode can you both read and write but the file is truncated?

The correct answer is "w+ mode" because it allows you to both read from and write to the file. When you open a file in "w+" mode, the file is created if it does not exist, and if it does exist, it is truncated to zero length. Truncating means that the existing contents of the file are cleared, making it suitable for starting fresh data while still enabling you to read from the newly emptied file after writing to it.

In contrast, "r mode" only permits reading from a file and does not allow any writing operations, making it unsuitable for tasks that require both reading and writing. "w mode" allows writing to the file while truncating it, but does not allow for reading the content. "a+ mode" lets you read and write to a file, but it appends to the end of the file rather than truncating it, preserving existing content.

In summary, "w+ mode" stands out because it fulfills the requirement of facilitating both read and write operations while also truncating the file, enabling a clean slate for the data.