The reason why ionic solids are hard is due to strong Columbic forces of attraction. But WHY ARE IONIC SOLIDS BRITTLE IN NATURE?
Kindly refer to the following link:
https://www.meritnation.com/ask-answer/question/how-we-can-say-that-ionic-solid-are-hard-and-brittle/the-solid-state/4611
https://www.meritnation.com/ask-answer/question/how-we-can-say-that-ionic-solid-are-hard-and-brittle/the-solid-state/4611