Question

Which decimal is closest to 1/6

Answer 1

The answer would be 0.166666667 1 divided by six is all you have to do

Answer 2

This definitely sounds like a question where there are
some choices listed but you decided not to share them.

Let's say you have several decimals that all look like this:

0.166
0.166666
0.1666
0.16666666666
0.16
.
.

The one with the most 6s is the closest to 1/6 .

Can you ever write a decimal that's exactly equal to 1/6 ?

No, you can't.  The 6s go on forever, and never end. 
The more 6s there are, the closer it is to 1/6, but it
can never be exactly 1/6 .