I am confused by the word "az" If you want to say "That is the apple"? Would you say "Az az almat (van)"? or would one "az" fall out?
You would need both of them. Az az alma. - That is the apple.
There are really two different words:
- The demonstrative az which means "that" (and always has its z), and
- The definite article a(z) which means "the" and appears as az before a vowel and a before a consonant.
If you let one az "fall out", as you say, and write "Az alma." as a sentence, then that means "That is an apple" or possibly "That is a bunch of apples." Without any article in front of it, alma could mean an apple or a mass quantity of apples.
Did the sentence change? I see ablak, not alma.
Anyway, "the one apple" could be translated as "az egyik alma".