Question

the outlined elements have a major characteristic in common. they are all
a metals.
b nonmetals.
c very reactive.
d solids at room temperature.

Explanation:

• Option A: The outlined elements (Ce - Cerium, Pr - Praseodymium, Nd - Neodymium, etc.) are all metals. Lanthanides (Ce - Lu) and actinides (Th - Lr) are metallic in nature.
• Option B: They are not non - metals. Non - metals have different physical and chemical properties like poor conductivity, etc., which these elements do not exhibit.
• Option C: While some of these metals can be reactive, it is not the most defining common characteristic. For example, compared to alkali metals which are extremely reactive, these lanthanides and actinides have a different reactivity profile.
• Option D: While they are solids at room temperature, this is a property that many metals (and some non - metals like carbon in diamond form) share. The more specific and defining characteristic is that they are metals.

Answer:

A. metals.