Question

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.

Answer 1

not June' but June?

not MArch but March

It has been 150 WHAT since the Italian, etc.

Sra

Answer 2

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.

:-)