As the message contains one truth, the third says that the gold is in the second box, if it is to be true, then the first box message will also become true. So Gold cannot be in second and third boxes. Gold is in the first box.

Our solution:

Toss the coin twice.

Let TH, HT and TT correspond to the three choices.

And if you get HH, just repeat (so it takes 8/3 tosses on average).

BIASED COIN

If the coin was biased, TH and HT would occur with equal probability.

So you could assign THHT, HTTH and THTH to the three choices, with other 4-toss outcomes rejected.

Or you could assign HTT, THT and TTH to the three choices, with other 3-toss outcomes rejected.

Our solution:

Take a piece of fruit from the "apples and oranges" crate. If it's an apple then you know that is the "apples" crate since ALL THE CRATES ARE LABELED INCORRECTLY. This means the crate marked "apples" must be "oranges" and the crate marked "oranges" must be "apples and oranges".