Which of the following is required for a properly labeled graph?
a: gridlines
b: a line that connects all of the points
c: a color-coded legend
d: a title

D. Title

Explanation:

It's the most essential part of the graph as without which the person could not know what information the graph wants to depict and how. The color codes are also essential but not as the heading on the graph. For proper labeling it one needs to keep in mind the x-axis and y-axis. and the labels below. From seeing the title one can easily make out whether one is reading a graph of climate change or rainfall or population growth over the years. The title thus has to be bold and accurately labeled in the center so as the readers can understand what is meant to convey.

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts