Why is a pencil used to mark the chromatogram instead of pen?

Chromatographic is actually one of the seperation techniques used to get pure compounds out of mixtures.
If a pen is used, this process will actually seperate the components of the ink inside the pen causing sopts and stains. On the other hand, this process cannot do this for the lead of the pencil.

It was ernest rutherford

The answer is c) pyrite