Bro, @Yash2 is considering another axis. We are saying that net torque about axis through C perpendicular to plane of paper is 0. Which is true.
But net torque for axis passing through C \perp PQ is what Yash has written on the paper.
But as far as I know, you can't say M \times B here, cuz M = iA is defined for current carrying loops as I mentioned earlier.