Are these last two senteces correct

Do you have to take a make-up exam if you fail a subject in June'
Do you know what festivity is celebrated on next 16 MArch in Italy
It has been 150 since the Italian republic was founded.

not June' but June?

not MArch but March

It has been 150 WHAT since the Italian, etc.

Sra

1st sentence is unclear. It sounds like you mean to ask:

Do you have to take a make-up exam in June if you fail a subject?

OR

If you fail a subject in June, do you have to take a make-up exam?

Putting "in June" at the end confuses what happens in June. (The failing or the exam).

"Do you know what festivity is celebrated on next 16 MArch in Italy"

You forgot a question mark. It might sound less awkward if you changed it around some. "Do you know what festivity is celebrated in Italy on March 16 of (this/next) year?" "On the next March 16" might be OK, but just sounds odd to me.

"It has been 150 since the Italian republic was founded."

150...Minutes? Hours? Days? Years? Decades? Centuries? :-)

I would also capitalize the r in republic.

:-)

To determine if these sentences are correct, let's analyze them one by one:

1. "Do you have to take a make-up exam if you fail a subject in June?"
This sentence is grammatically correct. However, it appears to be a question addressed to someone else, so it should be attributed to a specific person, for example: "Do students have to take a make-up exam if they fail a subject in June?"

2. "Do you know what festivity is celebrated on next 16 March in Italy?"
This sentence is also grammatically correct. However, there is a missing article before the word "next." It should be: "Do you know what festivity is celebrated on the next 16th March in Italy?" Additionally, the word "March" should be capitalized since it's a proper noun.

3. "It has been 150 since the Italian republic was founded."
This sentence contains a grammatical error. It should be: "It has been 150 years since the Italian Republic was founded." Additionally, "Italian Republic" should be capitalized since it refers to a specific entity, and there should be a comma after the word "150."

Remember that these suggestions are based on proper grammar usage, and context can sometimes affect the accuracy of the sentences.