How do I convert 31.5g of silver to cm3? Is it true for other substances besides water that 1g = 1cm3?

You need to know the density of silver to find the volume of 31.5 g Ag . ( V = m/d ). the density of water is 1 g/ 1 cm^3 or 1 g/ 1ml, so the mass of 1 g of water will occupy the volume 1 cm^3

1g =1cm³ is the density of water at 4°C , but it is generally used as a density value at normal temperature. I do not think that any other well known substance has exactly this density . Certainly not silver. The density of silver at room temperature = 10.5g/cm³

Use the density formula

density = mass / volume

rearrange to solve for volume:

volume = mass / density

volume = 31.5/10.5

volume = 3.00cm³