[EI88]

I haven't taken Chem in a year and I've forgotten alot of things. Taking AP Chem this year and doing summer assignment now. I'm stuck on a question:
Which of the following species is smallest in size?
A. Cl
B. I
C. Cl-
D. I-
I know the answer is A, but I would like to know how to get to that answer. Thanks for the help.

[JZ_1]

I dunno if this has any help....

http://xenon.che.ilstu.edu/genchemhelphomepage/topicreview/bp/ch7/size.html

Go down to the section with the name
"The Relative Size of Atoms and Their Ions"

[EI88]

Thanks