Solution (source code)

= Solution

The second-largest <eigenvalue> is $2$, with <eigenvector> $(1,-1,0)^{\mathsf T}$. A unit <principal component loading> is therefore
$$
\boxed{u_2=\frac1{\sqrt2}(1,-1,0)^{\mathsf T}}.
$$
It is <orthogonal> to the first loading $u_1=(1,1,\sqrt2)^{\mathsf T}/2$. Either sign of a loading is equivalent, provided its <principal component scores> use the same sign convention.