Q 11 is right .. The minimum length of the mirror should be half of that of the person
Reference :http://in.answers.yahoo.com/question...0043116AAYR7In

Q 46 is also right. The answer is water
Reference : Wikipedia

Q9: Quality
Reference : my sis and she is quoting her 9th standard Physics’s book by Punjab Board. If anyone could confirm that pls.
Another reference : http://hyperphysics.phy-astr.gsu.edu...timbre.html#c1

P.S : Thanks Zara for the effort and all those who took part in the discussion. Btw, where is the tab for thanking a post? Somehow, I couldn't manage to find it