Mentally challenged is no longer used.

Mentally challenged? What does this mean? Have a psychiatric diagnosis? Yes they can learn how to process information different, take medication, therapy, and more. Have an intellectual disability? Yes. Often people considered intellectually disabled are not pushed to achieve as much as they might and are deprived of opportunities. Given the opportunity to learn and be trained they can achieve mi=ore than they could before. Have a neurological disability? Often times these are more problematic in children and adults in a more flexible world than school can manage much better.

Mentally challenged is a made-up term used by people who can't face the reality of what they are experiencing - a disability. You challenge people in chess games.

Possibly

I suppose it really depends on specifically what the cause of their mental challenge is. I would think that a large portion of people that are mentally challenged are able to cope by learning specific techniques and can function normally under most circumstances.