Chemistry · Classification of Elements and Periodicity in Properties

What is the sign of ionization enthalpy for the removal of an electron from a gaseous atom?

1. Always positive (\( \Delta_i H > 0 \))
2. Always negative (\( \Delta_i H < 0 \))
3. Always zero (\( \Delta_i H = 0 \))
4. Can be positive or negative depending on the element