Barrons SAT Subject Test Chemistry, 13th Edition

(F, T) The oxidation state of carbon is often +4 but not always. Carbon does
have 4 valence electrons that it often relinquishes responsibility for in terms
of oxidation numbers (which is why carbon can have an oxidation state of
+4); however, it doesn’t have to do so, and in many compounds it exhibits a
different oxidation state.