Is Autism an intellectual disability? ?

It's a developmental delay. Some do have ID but most of them are very exceptional in academics, music, art, computers, memory, etc, however, they still have delays in social interaction. The disorder makes it hard to communicate and connect with other people because it's how their brain works.

No, it is a developmental disability. 

Autism is a neurodevelopmental disability that can occur by itself or concurrently with intellectual disabilities. And the number of people who have both an ID and an Autism disorder is around 10% of the population, not 70% Autism is also a spectrum of disorders, rather than just one alone.

And for AC, NO, Autism is NOT a mental illness, nor is it a disease. People with Autism aren't "sick" and we (I have mild Autism myself) aren't "broken". We don't need to be "fixed" or "cured".

Autism, on the other hand, is defined primarily by social difficulties, communication issues and repetitive behaviors. Yet intellectual disability comes with a suite of developmental delays that can include social differences, and that can lead clinicians astray.

Source: Google 

no..................there is no way to tell  how many autistics also have ID.  Many of the ones that can communicate and comply with the test, demonstrate average to above average skills, but for the ones with more severe symptoms that cannot comply with tests, it is impossible to get a IQ score.  I know people that would essentially test with an IQ of 0, but if you observe them when they are engaged, it will seem they at least have average IQ.

Yes it is a type of mental disorder.