Abstract noun.
Yes, the noun 'kindness' is a common noun, a general word for the quality or state of being gentle and considerate; a word for any kindness of any kind.
"Park Avenue" is a proper noun, because it is a place. Proper nouns like this should always be capitalized.
proper
common and proper
common
The noun 'kindness' is a singular, common, abstract noun.
common
It is a proper noun, because it is the name of a specific thing.
it's a common noun. a proper noun would be Spider-Man.
Proper
Pencil proper or common noun