Question

i am going to --------to the principal about this (complain,complaint )

Answer 1

I am going to complain to the principal about this.

After I am going to, clearly the verb form "complain " is to be used. "Complaint " is a noun. Alternately, we could write also as below:

I am going to WRITE A COMPLAINT to the principal about this.

Answer 2

Heyaa folk,

I am going to complain the principal about this.

Here, 'complaint' is a noun. And therefore, it is also the form of past participle. So we can't use 'complaint' here. Hence, we will use 'complain'.

Hope it helps u :)