Learn English – What do you think this number refers/refer to

In the sense of 'a thing or things that are owned by sb; a possession or possessions', (Oxford ALD) property is freqently used as a non-count noun.

In the sense of 'a building or buildings and the surrounding land' (OALD), property is used as a count noun.

When you're using a countable noun in the plural, further references to that noun should honor the plural:

Dogs are the loveliest (not most lovely) animals in the world.

In the singular, you would say:

Dog is man's best friend. (example: http://mashable.com/2013/03/12/dog-mans-best-friend/)

The + countable nouns is tricky. You'd typically use it when talking about a specific instance of the countable noun, not in general. So "the dog" isn't appropriate, since we're not talking about a specific dog. There are some cases where you use "the", for example - the Moon, the Sun, the equator. All of these words have plurals, but of all moons and suns there are some of special significance to us, and so we use a definite article there.