En el informe, la periodista comparó un número impar con uno par para explicar mejor los datos.

En el informe means in the report.

• en = in
• el informe = the report

This opening sets the context for the sentence: it tells you where the comparison appeared. Spanish often begins with this kind of time/place/context phrase.

You could also say:

• La periodista comparó... en el informe
  but putting En el informe first gives it a little more emphasis as the setting.

Periodista is a noun that usually has the same form for both masculine and feminine. The article tells you the gender of the person:

• el periodista = the male journalist
• la periodista = the female journalist

So in this sentence, la periodista shows that the journalist is a woman.

This is common with many Spanish nouns ending in -ista:

• el artista / la artista
• el dentista / la dentista

Comparó is the preterite form of comparar for él/ella/usted.

So:

• yo comparé
• tú comparaste
• él/ella comparó

The preterite is used because the sentence describes a completed action in the past: the journalist compared one thing with another.

The accent mark is important:

• comparo = I compare
• comparó = he/she compared

So the accent tells you both pronunciation and meaning.

With comparar, Spanish commonly uses con to mean with:

• comparar X con Y = to compare X with Y

So:

• comparó un número impar con uno par
  = she compared an odd number with an even one

This is the standard structure.

You may also sometimes see comparar X y Y, but comparar X con Y is especially clear and very common.

This is a very common and useful Spanish pattern.

In the first part, the full noun phrase appears:

• un número impar = an odd number

In the second part, Spanish avoids repeating número, so it uses uno to stand in for it:

• uno par = an even one

So the structure is basically:

• un número impar con uno par
• literally: an odd number with an even one

This uno is a pronoun replacing the noun número.

Compare:

• Tengo un coche rojo y uno azul.
  = I have a red car and a blue one.

Important:

• un is an article: a/an
• uno is a pronoun: one

Because here uno means one, standing in for número.

• uno par = an even one
• un par usually means a pair or a couple

So un par would mean something completely different.

That is why uno is necessary here: it replaces the omitted noun.

Because they are adjectives describing the noun número:

• número impar = odd number
• número par = even number

In Spanish, most descriptive adjectives normally come after the noun. So this word order is the normal one.

English often puts adjectives before the noun:

• odd number
• even number

Spanish usually does the opposite:

• número impar
• número par

Para expresses purpose or goal.

So:

• para explicar mejor los datos = in order to explain the data better

This tells us why the journalist made the comparison.

By contrast, por usually expresses ideas like:

• cause
• reason
• exchange
• movement through
• means

So here para is the correct choice because the comparison was done for the purpose of explaining the data better.

Both are possible in general, but they mean slightly different things.

• bien = well
• mejor = better

In this sentence, mejor suggests comparison: the journalist compared the numbers to explain the data better, probably better than she could without that comparison.

So:

• explicar bien los datos = explain the data well
• explicar mejor los datos = explain the data better

Also, mejor does not change form here because it is working as an adverb, modifying explicar.

Yes. Dato is a masculine noun:

• el dato = the datum / piece of data
• los datos = the data

So the article is los because:

• the noun is masculine
• it is plural

In everyday Spanish, datos is the normal word for data, figures, or information, depending on context.

The comma separates the introductory phrase from the main clause.

• En el informe, la periodista comparó...

This is very natural in Spanish when a sentence begins with a contextual phrase such as:

• En el informe, ...
• Ayer, ...
• Durante la entrevista, ...

The comma helps readability, though punctuation can sometimes vary depending on style.

Yes, Spanish word order is fairly flexible, though some versions sound more natural than others.

The original:

• En el informe, la periodista comparó un número impar con uno par para explicar mejor los datos.

Other possible versions:

• La periodista comparó un número impar con uno par en el informe para explicar mejor los datos.
• La periodista, en el informe, comparó un número impar con uno par para explicar mejor los datos.

The original version sounds very natural because it introduces the context first, then the subject, then the action.

Yes. Uno agrees with the noun it replaces, and número is masculine:

• un número → uno
• if it were replacing a feminine noun, you would use una

For example:

• una idea buena y una mejor
• un número impar y uno par

So uno is masculine because it stands for número.