Answer: Density
Explanation:
The mass of both materials is 20g yet the size of both materials are different which means that the space they occupy (volume) is different as well.
They therefore have different densities because Density is calculated by dividing mass by volume. As both materials each have a different volume, their resultant densities will be different. Indeed with A having a higher volume than B, it will have a lower Density than B.
