{c}

The derivative of the pair's total <angular momentum> is $q_1\times F-q_2\times F=(q_1-q_2)\times F=0$, since $F$ is parallel to the separation vector. Therefore \b[the combined <angular momentum> of particles one and two is conserved], despite the possible exchange between them individually.

Solution

Past exam of the probability, statistics and options I course of the University of Oxford / 2009 / H / 1 / iii / Solution

 Solution (source code)