Ok

[Hal_Al]

No, that is not correct. Grandma is allowed to claim him, simply because the child lives with her. A child can be the “qualifying child” dependent of any close relative in the household.  That relative has a higher claiming right than the non custodial parent (you).

That answer assumes that you do not live in the same home with the child and mother.

[NCperson]

the question never suggests who the child is living with.   

However, it is correct that the taxpayer that the child lives with is the one that can claim the child.  

[JesseSanchez0316]

My Son does not live with me but I do take care of him every weekend. 

[xmasbaby0]

"every weekend" does not make you the custodial parent.  The custodial parent is the one with whom the child spent the most nights during the year--at least 183 nights.