Question

I saw Veena.....the house. (Fill the blank with with infinitive)

I saw Veena leave the house. (Is this correct?)
I saw Veena leaving the house becomes a gerund.

Answer 1

yes

Answer 2

Yes. The infinitive, as you probably know, is the "to" form of the verb: in this case, "to leave." But many verbs take the infinitive minus its "to" marker in the predicate phrase, as does this one.

Other verbs retain it, as in --

I want Veena to leave the house.

I asked Veena to leave the house.