A Bar diagram is a

one-dimensional diagram 

The correct answer is Option 1 : One-dimensional diagram

A bar diagram, also known as a bar chart, represents data using rectangular bars where the length of each bar is proportional to the value it represents. The term "one-dimensional" here refers to the fact that the bars vary in only one dimension—length. While the bars themselves are two-dimensional objects (having both length and width), in the context of statistical diagrams, a bar diagram is considered one-dimensional because it primarily communicates information through the length of the bars, not their area. This is in contrast to two-dimensional diagrams like pie charts or area charts, which use both dimensions to represent data.