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In the circuit shown below, the knee current of the ideal Zener diode is $10\: mA.$ To maintain $5\: V$ across $R_{L},$ the minimum value of $R_{L}$ in $\Omega$ and the minimum power rating of the Zener diode in $mW,$ respectively, are

1. $125$ and $125$
2. $125$ and $250$
3. $250$ and $125$
4. $250$ and $250$