(a) Here,

According to the question,

We have to find the most popular pet among them.

Now,

Here,

The bar graph represents the pets owned by the students of class seven.

And,

We can see that,

The bar of the cat is the tallest

Hence,

Cat is the most popular pet.

(b) Here,

According to the question,

We have to find the number of students who have dog as a pet.

Now,

Here,

We know that,

The bar graph represents the pets owned by the students of class seven.

And,

We can see that,

The bar of the dog is till 8

Hence,

8 students have dog as their pet.