To calculate the volume given the density and mass, we can use the formula:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Rearranging this to solve for volume:

$\text{Volume} = \frac{\text{Mass}}{\text{Density}}$

Now, plug in the values:

$\text{Volume} = \frac{0.86 \, \text{g}}{3.5 \, \text{g/mL}}$

$\text{Volume} = 0.246 \, \text{mL}$

So, the volume is 0.246 mL.

Would you like a detailed explanation or have any further questions?

Here are some related questions:

1. How would the volume change if the density was doubled?
2. How do different units of mass and volume affect this calculation?
3. What is the relationship between mass, density, and volume?
4. How can we convert between grams and milliliters for different substances?
5. How do you calculate density if you only know the volume and mass?

Tip: Always check that the units of mass and density match up when performing calculations!