What Is the Minimum Energy an Incoming Electron Must Have $( n = 1 )$

Multiple Choice

What is the minimum energy an incoming electron must have to knock a K shell electron $( n = 1 )$ out of an atom of molybdenum, which contains 42 protons?

A) $44.0 \mathrm { keV }$
B) $34.4 \mathrm { keV }$
C) $24.0 \mathrm { keV }$
D) $10.1 \mathrm { keV }$
E) $11.3 \mathrm { keV }$