What is we have n=8?

#1

in 4*n, lets say n=8 , we fixed the first tile(vertically), then how can we say that there are (n-1) positions left ?
we can fix another tile over first tile in the same column.

#2

@premang
If we have placed one tile vertically
The now available coloum are n-1 as we placed one tile of width 1.

No ,Overlapping is not allowed.