Orthogonal functions and orthogonal matrices

Which of the following linear transformations $T:\mathbb{R}^{3}\to\mathbb{R}^{3}$ are orthogonal?

1. A rotation by 30 degrees about the $z$-axis.

2. A reflection about the plane $x=y$.

3. A scaling by a factor of $2$.

4. A scaling by a factor of $-1$.

Which of the following matrices define orthogonal transformations? Which ones define isometries?

Determine which of the following matrices are orthogonal by checking whether the columns form an orthonormal set.