Which of the following is a valid file identifier typically found in the header of a file?

A valid file identifier, often known as a "magic number," is a distinctive sequence of bytes at the beginning of a file that indicates its format or type. These identifiers help software recognize the file format quickly.

The identifier "%PNG" is specifically associated with PNG (Portable Network Graphics) files. When a program opens a file, it typically checks the magic number in the header to determine how to process the file. In the case of PNG files, the %PNG marker is a clear indicator that the file is in the PNG format, allowing for the correct decoding and rendering of the image.

The other options do not represent valid file identifiers. For instance, the sequence "~~~*PH" or "START__*___*PNG" do not correspond to any well-known file formats and would not be useful for identifying file types. Thus, recognizing "%PNG" as a valid file identifier illustrates an important concept in file management and software operation, enhancing the ability to distinguish between different file formats effectively.