HELP!!! Collisions covalent bonding level 16! Can someone solve this for me please?!!!

The kw for water at 0 °c is 0.12× 10–14 m2. calculate the ph of a neutral aqueous solution at 0 °c.

How many moles of potassium are needed to react completely with 12.8 moles of magnessium bromide?

A1.50-liter sample of dry air in a cylinder exerts a pressure of 3.00 atmospheres at a temperature of 25°c. without changing the temperature, a piston is moved in the cylinder until the pressure in the cylinder is reduced to 1.00 atmospheres. the volume of the gas is