In 6 there are 2 mistakes. It should be “The books are ours (not our’s (doesn’t exist, like her’s, your’s or their’s)), the notebooks are Thomas’s” (a word naturally ending in s has an apostrophe s after it). Bad question.
And in 5, I would point out that “t’s” is not a possessive, so should, in theory, have no apostrophe.
However, as ‘dot the is and cross the ts’ would be silly, it is often given as i’s and t’s, but to be properly correct it should be “dot the 'i’s and cross the 't’s” … though maybe that’s going too far.
