A gerund is that form of the verb which ends in—ing and has the force of a noun and ______________

The correct answer is: A verb

The Gerund has the force of both a noun and a verb. A gerund can be the subject of a sentence or the object of a verb, or it may be governed by a preposition.
Swimming is my favourite sport.
In the above sentence, the Gerund 'swimming' is the subject of the sentence.
I like baking cakes.
In the above sentence, the Gerund 'baking', like a noun, is the object of a verb. However, like a verb, it also takes an object, indicating that it has the force of a verb as well.
Lila is fond of knitting sweaters.
In the above sentence, the Gerund 'knitting' is governed by a preposition. However, like a verb, it also takes an object.