sorry for the repetitive questions! otherwise thank you for taking the time to check my answers.

Underline the gerund, some do not have a gerund if so write ''no gerund.''
1. Sketching is fun for me.
Sketching - Subject

2. Marya exercises every day by swimming.
Swimming - Object of preposition

3. She and I are singing in the chorus tonight.
No gerund

4. Of all my interests, I care most about reading.
Reading - object of preposition

5. Traveling comes second or third on my list of favorites.

Traveling - Subject

6. What is the most interesting hobby for you?
No gerund

7. Her other leisure activity is painting.
Painting - Predicate noun

3 answers

3 is wrong. The others are correct.
You're right. 3. does not have a gerund. Singing is part of the verb, are singing.

All are right.
I disagree on #3, and that's my story and I'm sticking to it. :)