Answer
21 mL
Work Step by Step
We find:
$M_{1}V_{1}=M_{2}V_{2}$
$(12.0\,M)V_{1}=(1.0\,M)(250\,mL)$
$\implies V_{1}=\frac{(1.0\,M)(250\,mL)}{12.0\,M}=21\,mL$
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