Tijdens de lunchpauze vergeet Tom zijn sleutelbos op tafel.

During the lunch break Tom forgets his bunch of keys on the table.

Breakdown of Tijdens de lunchpauze vergeet Tom zijn sleutelbos op tafel.

• Tom: Tom
• de tafel: the table
• zijn: his
• tijdens: during
• vergeten: to forget
• op: on
• de lunchpauze: the lunch break
• de sleutelbos: the bunch of keys

Questions & Answers about Tijdens de lunchpauze vergeet Tom zijn sleutelbos op tafel.

What does tijdens mean, and can I also say in de lunchpauze?

tijdens is a preposition meaning “during.” You use it with a noun phrase to indicate when something happens.
Examples:

• tijdens de film – during the movie
• tijdens het feestje – during the party

You can often replace tijdens with in (especially in colloquial speech):

• in de lunchpauze = tijdens de lunchpauze
  However, tijdens sounds a bit more formal.

Why is the finite verb vergeet placed before the subject Tom in this sentence?

Dutch is a V2-language, which means the finite verb always comes second in a main clause.
Structure here:
1) Tijdens de lunchpauze (time adverbial)
2) vergeet (finite verb)
3) Tom (subject)

If you start with the subject, you’d get Tom vergeet tijdens de lunchpauze..., which is also correct but shifts the emphasis.

Is vergeet in the present tense? How would I say “Tom forgot his keyring”?

Yes, vergeet is present tense (“Tom forgets”).
To talk about the past:

• Simple past: vergat → Tom vergat zijn sleutelbos op tafel.
• Perfect tense: heeft ... vergeten → Tom heeft zijn sleutelbos op tafel vergeten.

What exactly is a sleutelbos, and how is it different from a sleutelhanger?

• sleutelbos (literally “key bunch”) refers to a bunch of keys on a ring.
• sleutelhanger (literally “key hanger”) usually means the keychain itself (often decorative), sometimes including the ring.

In everyday speech they’re often used interchangeably, but strictly speaking sleutelbos emphasises the keys and sleutelhanger the ring or fob.

What function does zijn serve here? Does it mean “to be” or “his”?

In this sentence zijn is the third-person singular possessive pronoun meaning his.
It shows that the keyring belongs to Tom. Possessive pronouns replace the article, so you say zijn sleutelbos rather than de sleutelbos.

Why is it de lunchpauze and not het lunchpauze?

Dutch compound nouns take the gender/article of their headword. Here the head is pauze, which is a de-word.
So you get de pauze, de lunchpauze, de werkdag, etc.

Why is it op tafel and not op de tafel?

In Dutch you often drop the article in set-piece locative expressions when referring to a familiar or generic location:

• op tafel – on (the) table (where we always have lunch)
• aan tafel – at (the) table (to eat)

If you want to stress that it’s one particular table among many, you can still say op de tafel.

How can I replace zijn sleutelbos with a pronoun?

Since sleutelbos is a de-word and it’s a direct object, you use hem for “it”:
Tijdens de lunchpauze vergeet Tom hem op tafel.
You don’t use er here, because er is for quantities or vague locations (e.g., Er ligt iets op tafel).