Question

which are the instruments used to see a mark of something that was not visible to the naked eye?
microscope
mass spectrometer
cathode ray tube
phosphorescent screens

Explanation:

A microscope is used to view objects or marks too small to be seen with the naked - eye. A mass spectrometer is for analyzing the mass - to - charge ratio of ions. A cathode - ray tube is used in old - style TVs and monitors for displaying images. Phosphorescent screens are used to detect radiation or charged particles, but not for general non - visible marks like a microscope.

Answer:

microscope