as we know nutral atom have equal number of protons and electrons
from the give this element have 11 protons so if it is nutral it must have 11 electrons,but in the question this atom is charged this means it gains or losts certain amount of electrons , this atom has 11 proton and 10 electron from this we can understand this atom dicreases by 1 from its proton, this means it losts one electron .
when an atom lostes electron it's charge become positive with the number of electrons it lostes .
this atom lost 1 electron there fore it have +1 charge and become ion called cathion
