Which of the following elements will have the lowest first ionisation energy?

Which of the following s-block metals has the lowest first ionisation energy?

Which element has the lowest first ionization energy?

Which of the following isoelectronic ion has the lowest ionisation energy?

Which of the following ioelectronic ions have the lowest ionisation enthalpy ?

Which of the following ioelectronic ions have the lowest ionisation enthalpy ?

Which one of the following elements has lowest ionisation energy: H, Mg, Cs, B Report the Atomic number of that element.