What is the "en" in "Est-ce qu'il vaut mieux acheter un appartement ou en louer un?"

Question

The english meaning is "Is it better to buy an aparment or to rent one?". But literally, every words in English can be found in French, which makes "en" redundant, no?

Answer 1

Unlike one in English, un cannot be used alone here.

En is a pronoun that refer to appartement :

...ou en louer un. (or rent one of them)

means

...ou louer un appartement.

Similarly, we can't say:

Je veux un. (I want one)

but we say instead:

J'en veux un.