Question

select the correct answer.
consider the group 1a elements sodium (period 3), potassium (period 4), and rubidium (period 5). what would you predict about the ionization energies of these elements?
a. na < k < rb
b. na > k > rb
c. rb < na < k
d. na = k = rb

Explanation:

Step1: Ionization energy trend

Ionization energy decreases down a group.

Step2: Analyze the elements

Sodium (Na) is in period 3, potassium (K) in period 4, rubidium (Rb) in period 5. As we move down the group (from Na to K to Rb), atomic size increases. Outer - shell electrons are more shielded and less tightly held. So, ionization energy decreases. Thus, \(Na>K>Rb\).

Answer:

B. Na > K > Rb