Remember that electrons provide a negative charge and protons provide a positive charge. When these two things are 'balanced', the atom is 'stable', without charges (its charge is neutral).
But, if an atom loses an electron, the atom would be losing that negative charge, 'gaining' the positive charge, it becomes an ion.
Remember that cations are positive ions and anions are negative ions. In this case, the atom is losing an electron, so it has more protons that are positive charges, thus becoming a cation. The answer is a cation.