No quiero perder el billete del tren.

In Spanish, no normally goes directly before the conjugated verb, not before the infinitive.

• Conjugated verb: quiero (from querer)
• Infinitive: perder

So the structure is:

• No quiero perder… = I don’t want to lose…

Putting no before perder (quiero no perder…) is possible but changes the nuance: it sounds more like “I want *not to lose the ticket”, which is more marked/emphatic and less common in everyday speech. The natural way is *No quiero perder….

Spanish uses conjugated verb + infinitive for verb chains like “want to do”, “have to do”, “can do”, etc.

• querer + infinitive = querer hacer algo (to want to do something)
• No quiero perder… = I don’t want to lose…

Other examples:

• Quiero comer. – I want to eat.
• No quiero salir. – I don’t want to go out.

Quiero is the 1st person singular, present tense of querer:

• yo quiero
• tú quieres
• él / ella / usted quiere
• nosotros queremos
• vosotros queréis
• ellos / ellas / ustedes quieren

In No quiero perder el billete del tren, the subject is yo (I), so the correct form is quiero.

Spanish usually omits subject pronouns because the verb ending already shows who the subject is.

• No quiero perder el billete del tren. – natural, everyday Spanish
• Yo no quiero perder el billete del tren. – also correct, but now yo adds emphasis (e.g. “I don’t want to lose it (but maybe someone else does)”).

So both are grammatically correct; the version without yo is more neutral.

Spanish often uses the definite article (el, la, los, las) where English uses a possessive (my, your, his…), when it’s clear from context whose thing it is.

Here, el billete del tren is clearly your ticket (because you don’t want to lose it), so Spanish can simply say:

• No quiero perder el billete del tren.

If you really want to highlight possession, you can say:

• No quiero perder mi billete de tren. – I don’t want to lose my train ticket.

Both are correct; the choice depends on what you want to emphasize.

• el billete = the ticket (a specific one that we both know about)
• un billete = a ticket (non‑specific, just any ticket)

In real life you normally have one specific ticket for a given trip, so el billete del tren sounds natural: “the train ticket (for this trip)”.

You might use un billete in more general or hypothetical contexts:

• No quiero perder un billete que me cueste tanto dinero.
  I don’t want to lose a ticket that costs me so much money.

Spanish has obligatory contractions:

• de + el = del
• a + el = al

So:

• de el tren → del tren (must contract)
• de la estación (no contraction with la)

El billete del tren literally is “the ticket of the train”, but the natural English is the train ticket.

Yes, you can say:

• No quiero perder el billete. – I don’t want to lose the ticket.

Adding del tren makes it more specific:

• No quiero perder el billete del tren. – I don’t want to lose the train ticket (not, say, a bus or plane ticket).

Both are correct; it depends on how precise you want to be.

They mean different things:

• perder el billete del tren
  = to lose the train ticket (you misplace the physical ticket).

• perder el tren
  = to miss the train (you arrive late and the train has already left).

So:

• No quiero perder el billete del tren. – I don’t want to lose the ticket.
• No quiero perder el tren. – I don’t want to miss the train.

Yes, if it’s clear what lo refers to, you can use a pronoun:

• No quiero perder el billete del tren.
• No quiero perderlo. – I don’t want to lose it.

Both are correct. With a pronoun, Spanish allows two positions:

1. Before the conjugated verb:
   No lo quiero perder.
2. Attached to the infinitive:
   No quiero perderlo.

Both mean the same. The full version with el billete del tren is just more explicit.

The choice depends on region:

• Spain (Peninsular Spanish):
  The usual word is billete for transport:

  • billete de tren – train ticket
  • billete de avión – plane ticket

• Many parts of Latin America:
  boleto is more common:

  • boleto de tren, boleto de avión

• entrada: for entry to events/places:

  • entrada de cine – cinema ticket
  • entrada para un concierto – concert ticket

In Spain, for your sentence, billete (del tren) is the natural choice.

No, not in the same way.

• perder algo = to lose something

  • perder el billete – to lose the ticket

• perderse (reflexive) often means to get lost (a person, or sometimes an object that “gets lost” without specifying who lost it):

  • Me he perdido. – I got lost.
  • El billete se ha perdido. – The ticket has got lost / has gone missing.

In your sentence you are the one actively “losing” the ticket, so you need perder, not perderse:

• No quiero perder el billete del tren. ✔️
• No quiero perderme el billete del tren. ❌ (this sounds wrong in Spanish)

Yes, this is also correct:

• No quiero perder el billete del tren.
• No quiero perder mi billete de tren.

Differences in nuance:

• el billete del tren
  
  • Slightly more objective; just “the train ticket” already known in context.
• mi billete de tren
  
  • Explicitly highlights that it is your ticket.

Both are normal in Spain; the choice is stylistic.

Spanish word order here is very close to English:

• Subject (often omitted) – (Yo)
• Negation – no
• Conjugated verb – quiero
• Infinitive – perder
• Direct object – el billete del tren

So:

• (Yo) no quiero perder el billete del tren.

Other orders like No quiero el billete del tren perder are ungrammatical or extremely unnatural in modern Spanish.