If $V_{DC}=150V$ and Q $1$ has a maximum voltage rating of $220$ V $,$ what would be the appropriate breakdown voltage $V_z$ value of the Zener diode used in the following circuit shown in Figure Q$15?$

$($a$)50$ V

$($b$)100$ V

$($c$)150$ V

$($d$)200$ V

I understand that there must be a certain safety margin, the answer seems to be $($D$)$ from my point of view, but it would help alot if you could input key points and formulaes so that i can better relate to this topic, thank you.