If a block has a density of 1.8 g/ml, will it float?

NO, the block with density 1.8 g/ml will not float.

Explanation:

Density is the relationship between volume and mass, whereas buoyancy is the ability of an object to float. Its buoyancy influences the density of an object.  

For an object float its density should be less than the density of water.If the density is higher , then it will not be able to displace equal amount of water causing the object to sink.

Here the block with density 1.8g/ml would sink since its density is greater than the density of water. The density of water is 1g/cm cube,

wher is the rest of the question