Plz help giving 15 points and brainlest

What semimetal can form four single covalent bonds.

If 22.5 liters of oxygen reacted with excess of hydrogen, how many liters of water vapor could be produced?

Assuming complete dissociation of the solute, how many grams of kno3 must be added to 275 ml of water to produce a solution that freezes at -14.5 c? the freezing point for pure water is 0.0 c and k_f is equal to 1.86 c/m