Final answer:
The density of the lava sample is 3 g/mL.
Step-by-step explanation:
The density of a substance is calculated by dividing the mass of the substance by its volume. In this case, the mass of the lava is 45 g and its volume is 15 mL. To find the density, divide the mass by the volume:
Density = mass/volume
Density = 45 g/15 mL
By performing the division, we get:
Density = 3 g/mL
Therefore, the density of the lava sample is 3 g/mL, which corresponds to option B.