Learn Italian: Ci sono cento stanze in questo albergo. - There are one hundred rooms in this hotel.

In English we say "one hundred", but in Italian, 100 is just cento. You never say un cento. You only put numbers in front for 200, 300, and so on (like duecento, trecento).

Why do we use ci sono here?

Ci sono means "there are" and is used because we are talking about multiple things (cento stanze). If you were talking about just one room, you would use c'è, which means "there is".

What is the singular form of stanze?

The singular is stanza (room). Since it is a feminine word that ends in -a, its plural changes the ending to -e, becoming stanze.

Could I write quest'albergo instead of questo albergo?

Yes, you can! Because albergo starts with a vowel, Italians often drop the -o in questo and replace it with an apostrophe to make it flow better when speaking (quest'albergo). However, keeping them separate as questo albergo is also completely correct.