The word miss as a transitive verb also means "to notice or discover the absence or loss of" such as "When I got off the bus, I missed my watch" (The Free Dictionary).

In this sense, you can say "My watch wad missed" or "My watch got missed". Both the sentences are in the passive. They means that my watch was discovered missing. In formal writing or spoken English, we use " get" instead of "be" to form passives in the structure of get + past participle. For example, my watch got stolen = my watch was stolen.

On the other hand, we use "go" to mean become in the form of go + adjective. For example, he went mad.

In the sentence #2 presented by the OP, the word missing is an adjective. So it's correct grammatically if you say "The keys went missing". I think you can also use " get" in the sense of become i.e. the keys got missing.

So the sentences #2 and 4 are correct grammatically and mean the same thing, whereas the sentence #3 is not correct.

As for the sentence #1, it sounds to be correct, but it doesn't mean the same thing as the #2 and 4. Instead, it means that the keys were discovered missing.

The phrases "in the afternoon" and "in the evening" are similarly to the phrase "in the morning." It is possible to use them to refer to tomorrow afternoon, tomorrow evening, and tomorrow morning respectively. However, these phrases are dependent on context. Using them in the wrong way or at the wrong time will cause confusion -- or at least sound odd.

I go into detail in the sections below. Go to the bottom for a summary.

How to Use These Phrases

"In the morning," "in the afternoon," and "in the evening" are all used to describe approximate time frames. Though the exact day may be stated, the exact time is either unknown or unimportant.

There are several different ways to use these phrases as illustrated below.

Reoccurring or Routine Events

You can use the simple present tense with any of these phrases to describe events or situations that occur with some frequency.

For example:

I drink coffee in the morning, but I prefer tea in the afternoon. I am rarely thirsty in the evening.

Here the speaker is describing his (or her) habits. Each morning, he will drink coffee. Each afternoon, if he drinks something, it will likely be tea. During the evening, though, he is unlikely to drink anything since he rarely thirsty at that point in the day.

Statements like this tend to include a description of the frequency such as "always", "rarely", or "sometimes."

Past Events

You can use the past tense to describe events that happened during an approximate time frame on a specific day.

As an example, let's say a woman named Mary did the following things on December 25, 2018 (Christmas Day):

• 8:17 AM to 10:49 AM: Opened presents with her husband and children
• 1:21 PM to 5:05 PM: She and her family visited her parents
• 6:33 PM to 9:46 PM: She and her family visited her in-laws

To describe her day, Mary might say the following:

I was very busy last Christmas! My family opened gifts in the morning. We then visited my parents in the afternoon and my in-laws in the evening.

When describing the past, it's important to establish which day you are talking about. In my experience, no one ever uses "in the morning/afternoon/evening" unless a specific day has already been mentioned.

Future Events

You can use the future tense to describe events that will (or may) happen in the future. It is often used to describe someone's plans.

For example, let's say a man named John is planning his weekend. His itinerary for Saturday might be as follows:

10:00 AM to 12:00 PM -- Go fishing 2:00 PM to 5:00 PM -- Play golf 7:00 PM to 11:00 PM -- Hang out with friends at the bar

John might summarize his plans this way:

I'm going to have a nice, relaxing day on Saturday. I'm going fishing in the morning, playing golf in the afternoon, and hanging out with my friends at the bar in the evening.

When describing the future, specifying a day is optional. If a day has not been specified, the assumption is that you are referring to the next morning, afternoon, or evening. Depending on the time of day, that may mean today or tomorrow.

Why the Confusion?

Why is "I've got to go to work in the morning" acceptable but not "I've got to go to work in the afternoon" and "I've got to go to work in the evening"? All three phrases are grammatically correct, the later two are likely to be inappropriate for a number of reasons.

(By the way, you can shorten the phrase to "I've got work in the morning.")

First of all, English speakers tend to start work in the morning (i.e. prior to noon). Someone wouldn't say they are "going to work in the afternoon" (or evening) unless they had a shift that started late. However, anyone who starts work in the morning and leaves in the evening might say they "have work in the afternoon."

Secondly, the line between morning and afternoon is clearer than the line between afternoon and evening. "Afternoon" literally means "after noon" so it's clear that "in the morning" is referring to any time prior to 12:00 AM. Evening doesn't have as precise a starting point, so it's less clear when something is "in the afternoon" or "in the evening." For this reason, "in the afternoon" and "in the evening" aren't used as often.

Lastly, and most importantly, the meaning of these phrases can change depending upon the time of day. If it's 8:00 PM when you say "I've got work in the morning," it's clear you mean tomorrow morning. If you to say the same thing at 8:00 AM, it would be a little confusing, but most people would assume you meant "tomorrow morning" and not "this morning." However, if you were to say "I've got work in the afternoon" at 8:00 AM, people would assume you meant "this afternoon" and not "tomorrow afternoon" since "this afternoon" is the next time it will be the afternoon.

Examples

To clarify this point more, consider the following example. Bob and Alice are co-workers. Bob has come to Alice asking for help. Alice responds by telling him when she's available. Here are three ways the conversation might be worded (after Bob and Alice greet each other.)

Example #1

Bob: Can you help me with this task tomorrow? Alice: Yes. I have meetings in the morning, but I am free in the afternoon.

Example #2

Bob: Can you help me with this task? Alice: Yes. I have meetings tomorrow morning, but I am free in the afternoon.

Example #3

Bob: Can you help me with this task? Alice: Yes. I have meetings in the morning, but I am free in the afternoon.

In example #1, when Bob asks for help, he mentions tomorrow. This establishes "tomorrow" as the context for both "in the morning" and "in the afternoon." This conversation could take place at any time during the day because Bob makes it clear that he wants help tomorrow.

In example #2, when Alice responds, she mentions tomorrow by saying "tomorrow morning." This establishes "tomorrow" as the context for "in the afternoon." This conversation could also take place at any time during the day and be clear. However, Alice's response would only make sense if the conversation happened near the end of the work day (e.g. 4:00 PM.) In this case, Bob would assume Alice is busy for the remainder of the work day. If Alice responded the same way earlier in the day (e.g. 8:00 AM), she is omitting her availability for that day. There's a number of ways Bob might react. He might ask "Are you free today?", he might assume she is busy until tomorrow, or he might suspect she is trying to postpone helping him.

In example #3, neither mention tomorrow, today, or any other day. If the conversation happened at 8:00 AM, Bob would assume Alice meant "this morning" and "this afternoon." If the same conversation happened at 4:00 PM, Bob would assume Alice meant "tomorrow morning" and "tomorrow afternoon."

Summary

In short, "in the morning/afternoon/evening" can be used to describe:

• Something that happens on a reoccurring basis
• Something that happened on a specific day in the past
• Something that will happen on a specific day in the future
• Something that will happen the next time it is morning/afternoon/evening

I hope the explanation above clarifies how to use these phrases. They are a good example of how important context can be when speaking English.

When in doubt, you can say "this morning/afternoon/evening" or "tomorrow morning/afternoon/evening" instead.

If someone else uses one of these phrases and you aren't sure what day they are referring to, don't hesitate to ask! (Most native English speakers I know would prefer to clarify than be misunderstood.)