Classify each of the following observations as an example of eir
a) Liquid nitrogen boils at —196 °C.
b) Propane, leaking from a damaged tank, ignites easily.
c) Silver jewellery tarnishes (darkens) in air.
d) Spilled oil generally floats on the surface of water.
e) Meat darkens when it is heated on a grill.
f) Sulfur trioxide changes to sulfuric acid In the atmosphere.