1.

There's (o There is) a sofa in the bedroom.

2.

There are two sofas in the bedroom.

3.

Is there a sofa in the bedroom?

4.

Are there two sofas in the bedroom?

5.

There's not (o There isn't / There is not) a sofa in the bedroom.

6.

There aren't (o There are not) two sofas in the bedroom.

7.

There are some sofas in the bedroom.

8.

There's (o There is) no sofa in the bedroom  
o también...
There are no sofas in the bedroom.