Answer
See answer below
Work Step by Step
We are given $S=\{A \in M_2R:$ A is orthogonal$\}$
Assume that $S=\begin{bmatrix}
0 & 0\\
0 & 0
\end{bmatrix} \notin S \rightarrow $
We can notice that $S$ is the zero vector $M_2(R)$ and every subspace of a vector space $S$ contain the zero vector of $S$.
Hence $S$ is not a subspace of $M_2R$
