1. Anyone/Someone called for you earlier, but I don't know who.
2.Can I ask you anything/something!
3. There's anyone/someone on the phone to speak to you.
4. Sorry, I don't know anything/nothing about it.
5. No one/Someone knew what to do, so I used my own initiative.
6. There's anything/nothing in the post for you this morning.

1. Anyone/Someone called for you earlier, but I don't know who.

For this question, the correct answer is "Anyone." We use "anyone" when we want to refer to any person in a general sense, without knowing or specifying their identity. In this context, the speaker is unsure about the identity of the person who called.

2. Can I ask you anything/something!

In this case, the correct answer is "anything." When we want to show that there are no restrictions or limitations on the questions we can ask, we use "anything." It means that the person can ask about any topic or any question they have in mind.

3. There's anyone/someone on the phone to speak to you.

The correct answer here is "someone." We use "someone" to refer to a particular or specific person, but without specifying the identity. In this sentence, it means that a person is waiting on the phone to speak with you.

4. Sorry, I don't know anything/nothing about it.

The correct answer is "anything." When we want to express a lack of knowledge or information about something, we use "anything." In this case, the speaker is apologizing for their lack of knowledge on the subject.

5. No one/Someone knew what to do, so I used my own initiative.

The correct answer is "No one." We use "no one" when we want to say that nobody or not a single person knew or had the knowledge or answer to a particular question or situation. In this sentence, it means that nobody knew what to do, resulting in the speaker taking their own initiative.

6. There's anything/nothing in the post for you this morning.

The correct answer is "nothing." When we want to express the absence of something or when there is nothing present or available, we use "nothing." In this sentence, it means that there are no letters or packages for you in the mail today.