Final answer:
The music album type known for expressing a particular theme or idea that rose to popularity in the 1960s and 70s is the concept album. It aligns with the era's artistic movements such as Pop Art and conceptual art, which prioritized ideas and themes over conventional forms.
Step-by-step explanation:
The kind of music album that became popular in the 1960s and 70s, known for expressing a particular theme or idea, is a) Concept album. The concept album is a type of album characterized by its thematic coherence, with songs usually unified by a single theme or a narrative. This form of album became increasingly popular during the psychedelic era, where artists like Pink Floyd with 'The Dark Side of the Moon' and The Who with 'Tommy' explored complex themes and storytelling in their work.
The rising popularity of concept albums in this era was concurrent with movements in the visual arts, such as Pop Art and conceptual art. Pop Art often challenged traditional fine art by including imagery from popular and mass culture, while conceptual art focused on the ideas and concepts behind the art rather than the physical object. Both movements strived to break from the confines of conventional artistic expression and resonate with a wider audience, just as concept albums aimed to offer a richer, more immersive experience to music listeners.