Question

the element with the smallest ionization energy in period 6 is - (options: os, cs, rn, tm)

Explanation:

Step1: Recall ionization energy trend

Ionization energy generally decreases down a group and increases across a period. In a period, metals (left side) have lower ionization energy than non - metals (right side).

Step2: Identify elements in Period 6

• Cs (Cesium) is an alkali metal (Group 1) in Period 6.
• Os (Osmium) is a transition metal (Group 8) in Period 6.
• Rn (Radon) is a noble gas (Group 18) in Period 6.
• Tm (Thulium) is a lanthanide (inner - transition metal) in Period 6.

Among these, alkali metals have the lowest ionization energy in a period because they have only one valence electron which is relatively easy to remove. So Cs has the smallest ionization energy in Period 6.

Answer:

B. Cs