THE ANSWER of qustion 2 is given below but I can not understand the answer. Please clarify the answer for me, thank you

2. Consider the market for guns in Australia. Assume that because some of these guns fall into the hands of criminals, there is a negative consumption externality. Illustrate this market on a diagram, and explain the resulting DWLfrom the market outcome. What is a possible government intervention from the government? Under what circumstances would the optimal level of guns traded be zero? Explain. See lecture notes on negative consumption externalities. For zero trade to be optimal the negative consumption externality at q = 0 needs to be at least as large as the gap between the PMB curve and the PMC curve