In a convection current, as the temperature of a fluid increases, its decreases.

In a convection current, as the temperature of a fluid increases, it's DENSITY decreases. 

When a fluid is heated, it expands. With expansion, the density of the fluid decreases and the fluid starts to rise up. As the fluid rises up, it cools and so its density decreases and it starts to fall down.
This process repeats as long as the fluid is being heated. That's why we have a convection current. 

Friction is the force that act and opposes all motion of moving objects

Is there any opitions? if you have the periodic table, the noble gases are 8a family, the halogen are the 7a family, and the nonmetal are  carbon, nitrogen, phosphorus, oxygen, sulfur, selenium, fluorine, chlorine, bromine, iodine and astatine.