Which sentence correctly uses an apostrophe?
- The dog wagged it's tail happily.
- Its a beautiful day for a walk.
- The company changed its logo last year.
- I think its going to rain later.
Why C? And why not the others?
Correct answer: C. The company changed its logo last year.
The word 'its' with no apostrophe is a possessive pronoun, part of the same small family as 'his', 'hers', 'ours', and 'theirs' — and none of those possessive pronouns ever take an apostrophe, even though every one of them shows ownership. An apostrophe only belongs in 'it's' when the word is a contraction standing in for 'it is' or 'it has', never when it means 'belonging to it'. That is exactly why the sentence about the company's logo is correct: 'its logo' means 'the logo belonging to it', a straightforward possessive with no contraction involved, so no apostrophe is needed. The sentence about the dog gets this backwards, adding an apostrophe to a possessive ('it's tail' should be 'its tail'). The two sentences about the weather make the opposite mistake: 'its a beautiful day' and 'its going to rain' are both really saying 'it is', which requires the contraction 'it's', so leaving the apostrophe out there is the error.
Source: Oxford English Dictionary entry for 'its'; BBC Bitesize KS3 English: Apostrophes