Why the marks of chalk on the blackboard are unable to be wiped out easily after a long time?

Why the marks of chalk on the blackboard are unable to be wiped out ea

1.	Why the marks of chalk on the blackboard are unable to be wiped out easily after a long time?
Answer» It is so because little bit PARTICLES of chalk gets diffused into the BLACKBOARD and HENCE are difficult to remove. You can EVEN try it. HOPE IT HELPS U☺☺☺