Spin singlet state
= Spin singlet state
{title2=$|\Psi^-\rangle$}
The two-spin singlet is
$$
|\Psi^-\rangle=\frac{|01\rangle-|10\rangle}{\sqrt2}.
$$
Spin measurements along axes $\mathbf a$ and $\mathbf b$ have correlation $E(\mathbf a,\mathbf b)=-\mathbf a\cdot\mathbf b$, and equal axes give perfect anticorrelation.
This is the <spin-one-half singlet state>, an example of an <angular momentum singlet state>. The general singlet condition is zero total angular momentum, not the choice of a particular two-qubit Bell basis.