What is the principal quantum number for the outermost electrons in a te atom in the ground

Principle Quantum number explains the main energy level, in other words it represent the main shell. It is represented by "n". Greater the value of n greater is the distance from nucleus.

Principle Quantum Number of Tellurium (Te):
                                                                      Electronic Configuration of Te is as follow,
                                        [Kr] 4d¹⁰, 5s², 5p⁴

It is shown in electronic configuration of Te that the valence electrons are present in 5th shell.

Result:
          As valence electrons are present in 5th shell, so the Principle Quantum Number for the outermost electron of Te is 5.

                                                       n  =  5

Gallium melts near room temperature and has one of the largest  liquid  ranges of any metal, so it has found use in high temperature thermometers.