Number of students in class shows an example of a discrete graph. Hence the correct option is b.
A discrete graph represents data that can only take distinct, separate values. In the context of the options provided, the number of students in a class is an example of discrete data. This is because the number of students is counted in whole numbers, and there are clear, distinct boundaries between different possible values (e.g., 25 students, 30 students).
On the other hand, a dog's weight and a person's height (options A and C) are continuous variables, as weight and height can take on a wide range of values and are typically measured on a continuous scale. Discrete data is characterized by countable and distinct values, making the number of students in a class a fitting example of a situation that can be represented by a discrete graph. Hence the correct option is b.