100 ml
100 ml of the stock solution is required to prepare the order.
We know that C1V1 = C2V2
where C1= 2%
V1 = 500ml
C2= 10%
V2 = ?
V2 = C1V1 / C2
= 500 * 2% / 10%
=100
V2 = 100 ml
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