Which of thses is correct?
Which of these is correct, "on Friday morning" or "in Friday morning"?
I'm confused about this two for a long time.

Question

Which of  thses is correct?
Which of  these is correct, "on Friday morning" or "in Friday morning"?
I'm confused about this two for a long time.

Answer

"On" is used for days (on Monday, Tuesday, etc.), "In" is used for the time of day (in the morning, in the evening, etc.)
So, "on Friday morning" is correct because the emphasis is put on Friday.

Answer

IN the morning but ON Friday morning.