What causes the earths crust to spread

Seafloor and tectonic plates.

Explanation: Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle's convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor

What is the mole fraction of a solution that contains 200 g of magnesium hydroxide in 225 g of water

0.215

Explanation:

Given parameters:

Mass of magnesium hydroxide = 200g

Mass of water = 225g

Unknown:

Mole fraction of solution = ?

Solution:

The mole fraction is a measurement of concentration that expresses the number of moles of solute to that of solution.

  Mole fraction =

A solution is made up of solute and solvent

Number of moles  =

Molar mass of Mg(OH)₂ = 24.3 + 2(16 + 1) = 58.3g/mol

Molar mass of H₂O = 2(1) + 16 = 18g/mol

Number of moles of Mg(OH)₂  =  = 3.43moles      solute

Number of moles of  H₂O  =   = 12.5moles              solvent

Mole fraction  =  = 0.215