The ions in materials such as chalk and other ionic compounds are bonded by electrostatic forces. These features give ionic compound unique characteristics. This includes the fact these materials are usually hard, which means they do not deform easily and the fact these are brittle, which means they break easily.
These properties can be observed in chalk because the chalk itself keeps its shape or does not deform (hardness) but it breaks easily under pressure (brittleness), indeed due to this last property it is possible to write using chalk and due to the first property it is possible the chalk is a durable material.
The ratio 1:2 means there are twice as many dimes as there are quarters. An expression could be n=2d, n being number of quarters, d being number of dimes.
