Final answer:
The most effective way to visually represent the grades of 31 students on a quiz is through a bar graph, as it allows for clear comparison of individual scores and avoids the potential clutter of a pie chart with many categories.
Step-by-step explanation:
To visually describe the grades of 31 students on a quiz, it is important to choose the most appropriate graph that clearly communicates the data. Among the given options, a bar graph would be the most effective choice.
This graphical representation allows for comparison of discrete categories or individual scores, making it suitable for displaying the distribution of quiz grades across all students in the class. While a pie chart could feature the proportion of grades, it might become cluttered and hard to interpret with too many categories. A line graph is typically used for displaying data that changes over time and a scatter plot is best for showing the relationship between two different variables.
Since we are dealing with individual quiz grades that are categorical and not over a period of time or in relation to another variable, a bar graph would be the clearest choice to show how many students received each possible score on the quiz.