Its just fun to test yourself, don't take it too seriously.
2: 2 (each with many facets and lenses).
4: 1 except mule which has no offspring.
6: A fish (species of Macheral).
7: Oak, hazel and Apple.
9: Cabbages grow above ground.
10: Black on White.
11: It squirts water into it's mouth.
12: a: Hippopotami or Hippopotamuses, b: Reindeer, c: Grouse, d: Mongooses.