Answer
$\mathbf{v}$ and $\mathbf{w}$ are orthogonal.
Work Step by Step
Dot product of $\mathbf{v}$ and $\mathbf{w}$ can be obtained as,
$\begin{align}
& \mathbf{v}\cdot \mathbf{w}=\left( \mathbf{i+j} \right)\cdot \left( \mathbf{i-j} \right) \\
& =1\cdot 1+1\left( -1 \right) \\
& =1-1 \\
& =0
\end{align}$
As the dot product of $\mathbf{v}$ and $\mathbf{w}$ is zero, thus, $\mathbf{v}$ and $\mathbf{w}$ are orthogonal.
Hence, $\mathbf{v}$ and $\mathbf{w}$ are orthogonal.