Qual è la differenza tra [Un ragazzo] e uno ragazzo ?Sentiti libero di rispondere con un esempio.

“Un ragazzo” (a boy) is right.
“Uno ragazzo” (literally one boy) is wrong.

For the indefinite masculine article “un” and “uno” the rule is this:
"Un” is always used even in front of words that start with a vowel, for example: un amico, un albero…

"Uno" is only used in front of words starting with:
- the consonant groups “gn”, “pn” and “ps”, for example:
uno gnomo, uno pneumatico, uno psicologo, uno spazzino
- words starting with “x” and “z”, for example:
uno xenofobo, uno zerbino.
- words that begin with “s”followed by another consonant, for example: "uno studio"
But in front of the "s" followed by "vowel", "un" is used instead, for example: un secchiello.

In all other cases we use “un”.

https://siti.italofonia.info/italianocorretto/2...