A zener of power rating 1W is to be used as a voltage regulator . If Zener has a breakdown of $5V$ and it has to regulate the voltage which fluctuated between $3\;V$ and $7\;V$, What should be the value of $R_s$ for Safe operation .

Question

$\begin{array}{1 1} 10\;\Omega \\ 5\;\Omega \\ 20\;\Omega \\ 15\;\Omega\end{array}$