Grindability of a material does not depend upon its

Standard textbooks like McCabe say:
Grindability mainly depends on hardness and toughness, and elasticity does NOT affect grindability.
Size has a secondary effect, but it is generally not considered a fundamental property affecting grindability.

If your book says "size" affects grindability, it might mean:

The feed particle size affects the grinding rate or efficiency in practice.

But grindability as a material property is usually defined independent of size.

To conclude:
If the question asks what grindability does not depend on, standard answer is:

Elasticity (because it's unrelated to fracture or crushing).

Size can influence grinding operation practically, but is less fundamental as a grindability property.