This apple is a countable noun.

This plan is unrealistic.

Since it started raining, I opened my umbrella.

He was a very excellent student before he turned to delinquency.

He is receiving countless blessings.

'Apple' is a count noun, and you can count it as one, two, etc.

Happiness is a mass noun, you can't count it.

He was called an unpatriotic person because of his actions.

She publicly acknowledged that she is asexual.

This is an unofficial meeting.