Please answer! I don't understand this so I need explanation.

  1.2×10^7 dm³

Explanation:

1 mole of sulfur dioxide weighs 64 grams, so 64 tonnes is 10^6 moles.

The reaction of interest is ...

  2SO₂ +O₂ ⇆ 2SO₃

This reaction uses half as many moles of oxygen as of sulfur dioxide. That is, 5×10^5 moles of oxygen are required. That quantity will have a volume of ...

  (5×10^5 mol)(24 dm³/mol) = 1.2×10^7 dm³ . . . volume of oxygen needed

"hydrogen bonding is the attraction of h atoms in the water molecule (slight + charge) to o atoms in a neighboring water molecule (slight - charge); it is a weak interatomic force. but it is still strong enough to the water molecules "stick" together."