1. The book is so popular that it is now in its tenth printing. 2. I prefer going out to watching TV at home. 3. No real difference. "On Sunday" without 's' could mean "I plan to go to church this Sunday," but it could also mean the same as "I go to church on Sundays" if you are describing your weekly schedule.

Hi, in my opinion: 1. The book is so popular that it is now 'in its' tenth printing. 2. I prefer going out 'over' watching TV at home. 3. I go to church on Sunday suggests the speaker goes to church every Sunday. However, I go to church on Sundays suggests that the speaker usually goes to church on Sundays, but not necessarily each and every Sunday. Cheers Syed