If you are looking for straight apostrophe '
(U+00027), it is
'
or '
(latest is HTLM 5 only)
If you are looking for the curly apostrophe ’
(U+02019), then yes, it is
’
or ’
As of to know which one to use, there are great answers in the Graphic Design community: What’s the right character for an apostrophe?.