Ég vel það fyrsta.

Vel is the 1st person singular present tense form of the verb velja (to choose).

So:

• að velja = to choose
• ég vel = I choose
• þú velur = you choose
• hann/hún/það velur = he/she/it chooses

This is one of those Icelandic verbs where the present-tense form does not look exactly like the infinitive, so learners often have to memorize it.

Here það fyrsta means the first one or that first one, depending on context.

Icelandic often uses a pronoun plus an adjective/ordinal to stand in for a whole noun phrase when the noun is understood.

So instead of saying a full noun like:

• Ég vel það fyrsta epli. = I choose that first apple.
  (not the most natural example, but it shows the structure)

you can simply say:

• Ég vel það fyrsta. = I choose the first one.

The noun is left out because it is already clear from context.

Because Icelandic usually does not need to say one in this kind of sentence.

English says:

• the first one

but Icelandic can just say:

• það fyrsta

The idea of one is understood automatically. This is very common when talking about options, items, choices, answers, and so on.

Because fyrsta has to agree with það (and with the implied noun) in gender, number, and case.

Here it is neuter singular, so the form is fyrsta.

A useful comparison:

• þann fyrsta = the first one (masculine, accusative)
• þá fyrstu = the first one (feminine, accusative)
• það fyrsta = the first one (neuter, accusative)

So fyrsti would be the masculine nominative form, which does not fit this sentence.

It is the direct object of vel, so it is in the accusative case.

The verb velja normally takes an accusative object:

• Ég vel bókina. = I choose the book.
• Ég vel það fyrsta. = I choose the first one.

In this sentence, það is neuter singular, and for neuter singular the nominative and accusative look the same, so you do not see a form change. But grammatically, it is still accusative.

Yes — it is the same Icelandic word, but its exact meaning depends on context.

Það can mean:

• it
• that
• or be part of a phrase that English translates more naturally as the ... one

In Ég vel það fyrsta, it is not best understood as a simple standalone it. Instead, it helps form the idea the first one / that first one.

So the most natural English translation is usually the first one, even though Icelandic uses það.

Usually no, not in standard Icelandic.

You normally need something to support the adjective/ordinal if there is no noun after it. That is why það fyrsta works: það acts as the pronoun standing in for the missing noun.

So:

• Ég vel það fyrsta. = correct
• Ég vel fyrsta. = generally not correct as a complete phrase

If the noun is actually stated, then of course you can use the adjective with it:

• Ég vel fyrsta kostinn. = I choose the first option.

This is the normal neutral word order for a simple main clause:

• subject
  • verb
    • object

So:

• Ég = subject
• vel = verb
• það fyrsta = object

Icelandic does allow other word orders for emphasis, contrast, or style, but Ég vel það fyrsta is the plain, natural way to say it.

They are two different sounds that English speakers often notice right away.

• þ is like the th in thing
• ð is like the th in this

So in this sentence:

• það begins with the sound from this
• there is no þ in það, but there is a ð
• fyrsta has neither þ nor ð
• Ég is roughly like yeg with an y sound at the start
• vel sounds roughly like veh-l
• það fyrsta is roughly thath first-a
  (very rough English approximation only)

As usual, the exact Icelandic pronunciation is a bit different from English, but those th comparisons are a good start.

In normal context, Ég vel það fyrsta is understood as I choose the first one.

However, like many short sentences, the exact nuance depends on context:

• it could mean I choose that first one
• or simply I pick the first one

What matters most grammatically is that það fyrsta refers to an understood item or option. So the sentence is about choosing the item that is first in some set.