Answer
a. lithium, boron
b. magnesium, strontium
c. cesium, aluminum
Work Step by Step
a. First ionization energy generally decreases when moving down a group and increases when moving across a period from left to right. Both boron and lithium are in the second period, but boron is on the right side. Therefore, the first ionization energy of boron is greater.
b. Magnesium and strontium are both in group 2A. Strontium is two period below magnesium, therefore magnesium has a greater first ionization energy.
c. Cesium is on the very left and (almost) the very bottom in the periodic table.
