NOTE: Any spell-check program ought to catch most of these for you. However, the wisest course is to master them yourself.
For fun, I did a search for the incorrect version of nine of the ten. I didn’t bother with Number 7 because both its and it’s are valid spellings. The number of hits for the misspellings is shown in parentheses. Some refer to intentional misspellings on English sites like this one, but not all.
The verb is argue, but the noun is argument.
The register on which you schedule your appointments is spelled calendar. Yes, there is a specialized term spelled calender that refers to paper production, but I doubt that it accounts for millions of uses.
There are three e’s in cemetery. Nary an a in sight.
Think, finite, infinite, infinity. Look at all those i’s. No a’s anywhere in definite.
The adjective is final. The adverb is finally. Double that l in finally.
One less than five is spelled four. One more than thirty-nine is spelled forty.
7. its (possessive adjective)
The problem with this habitual misspelling is that both its and it’s are English spellings. It’s is a contraction of the words “It is.” Its is a possessive adjective, like his. The best advice is to spell out “it is” when that is your meaning. You cannot rely on grammar/spell checkers to catch this one. Indeed, Word often advises me to write “it’s” when the context calls for its.
Take the word by syllables: sep-a-rate. Yes, we pronounce it [sep-uh-ret], but we spell it sep-a-rate. Look for “a rat” in sep.a.rat.e.
The g in tragedy is soft. The e makes the g soft. No extra d, please.
The adjective is true. The adverb is truly.