Hey,
One common way to spot an intensive property is that they are a ratio of two extensive properties.
The key here for density being an intensive property is that it is m/V.
Using the example of water, if you were to calculate the density of 1g = 1 mL of water, it would be:
1g/1mL = 1 g/mL.
If you then tried to do the same for 2g = 2mL of water, your density would be:
2g/2mL = 1 g/mL.
You get the intensive nature of density because when you add mass, you must also be adding volume, so your overall density should remain the same.
Many intensive properties are given in this x/y format, for example molar mass and pressure.
Please let me know if this is unclear.