Answer:
![V_1=2mL](https://img.qammunity.org/2021/formulas/physics/college/gus7mx60zjo36bwe22hobihz73lszeyg5i.png)
Step-by-step explanation:
Hello,
In this case, considering this as a dilution problem, the first step here is to consider that the moles of tetrodotoxin remains the same and just the volumes and concentrations are modified from the initial stock (1) and the required dilution (2):
![V_1M_1=V_2M_2](https://img.qammunity.org/2021/formulas/biology/high-school/itwod5cuco4gy4t3p9l9bcmrtof8cw7gl9.png)
Whereas V is referred to volume and M to molar concentration, in this case in mM. In such a way, solving the V1 as the volume of the 3-mM solution we obtain:
![V_1=(V_2M_2)/(M_1) \\\\V_1=(6mL*1mM)/(3mM) \\\\V_1=2mL](https://img.qammunity.org/2021/formulas/physics/college/8be71wltruc5dor1k659ckux6ogvtpfomw.png)
It means you need 2 mL of the 3-mM solution.
Best regards.