can you please help me to figure out this question?

Question

The grid in a high-vacuum triode is usually kept negatively charged with respect to the cathodes so that the electrons may be?

Answer 1

electrons may be present around it in a dynamic fashion. This is called space charge. As grid is situated near the cathode the source of electrons and inside the space charge it is able to control the flow of electrons to the anode in more effective manner.