= Solution
Let $\mathbf F$ be the force on particle one, so the force on particle two is $-\mathbf F$, with $\mathbf F$ parallel to $\mathbf q_1-\mathbf q_2$. The combined <torque> is
$$
\mathbf q_1\times\mathbf F+\mathbf q_2\times(-\mathbf F)
=(\mathbf q_1-\mathbf q_2)\times\mathbf F=0.
$$
Hence \b[the combined <angular momentum> of particles one and two is conserved]. Centrality of their interaction, in addition to equal and opposite forces, is what makes this <torque> sum zero.
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