I'm currently working on open world game. But I am confused about one thing that, is it ok if I put real monuments and sculptures like white house, statue of liberty etc. in my game? Please help if anyone knows and confident about his/her answer. Thanks in advance!
It looks like there might be some restrictions on certain monuments, but not the ones that you asked about at least.
According to this, which granted is about photography and not games specifically, some famous monuments have restrictions on using them for commercial purposes, but from what I know of copyright laws, this could also translate to using them in games for commercial purposes. Although, as I said above, the monuments that you mentioned are not included in these restrictions, so you should be safe to use them.