  Given a graph $G=(V, E)$ and a positive integer $k$, in Maximum $k$-Order
Bounded Component Set (Max-$k$-OBCS), it is required to find a vertex set $S
\subseteq V$ of maximum size such that each component in the induced graph
$G[S]$ has at most $k$ vertices. We prove that for constant $k$, Max-$k$-OBCS
is hard to approximate within a factor of $n^{1 -\epsilon}$, for any $\epsilon
> 0$, unless $\mathsf{P} = \mathsf{NP}$. This is an improvement on the previous
lower bound of $\sqrt{n}$ for Max-2-OBCS due to Orlovich et al. We provide
lower bounds on the approximability when $k$ is not a constant as well.
Max-$k$-OBCS can be seen as a generalization of Maximum Independent Set
(Max-IS). We generalize Tur\'an's greedy algorithm for Max-IS and prove that it
approximates Max-$k$-OBCS within a factor of $(2k - 1)\overline{d} + k$, where
$\overline{d}$ is the average degree of the input graph $G$. This approximation
factor is a generalization of Tur\'an's approximation factor for Max-IS.
