Interior of the set {1/n} What is the interior of the set {1/n} where n is a natural number?
For me by considering the definition I think the interior is an empty set.Am I right here?

The interior of a set is the union of all open sets contained in the set. This really depends on the topology you consider on $K=\{\frac{1}{n}|n\in\mathbb{N}\}$, but assuming you are considering $K\subset\mathbb{R}$, with the standard topology.
In which case, $K$ contains no open sets, and thus yes you are correct and the interior is empty.
