Why are some liquids more viscous than others?

The force that opposes the movement of an object through water is called drag. This is a type of frictional force. This force normally depends on the density and the viscosity of the fluid in question. The liquid which has more density and more viscosity or stickiness will produce a greater amount of drag force on an object than a fluid that is less dense and less viscous in nature.  River water normally has less drag than that of sea water.  

The thrown pebble hits first

The dropped pebble hits first

They hit at the same time

We cannot tell without knowing which pebble is heavier